Whatever wars Christians have fought amongst themselves over whose creed is the correct one, (and history has its own bloody record there), virtually all parties have universally agreed to the above: it is the very bedrock foundation of Christianity, the Church, itself. Diverging from this is the Bible's definition of "heresy."

From the beginning of the Gospel there have been people who insist that, in order to understand the Will of God, there are more writings needed besides the Scriptures. Whether it be special teaching, special teachers, or special writings or special decoders, some people have always insisted upon something more than the Bible itself, something more than the Word & Spirit of God Almighty.

In the days of Jesus' first appearrance, there were the Pharisees and their traditions, the so-called "Oral Law," (Midrash), that was put to writing by the Scribes & Pharisees during the same period as the New Testament, the first century AD. Jesus denounced their extra-biblical traditions as distracting people away from the power of the Word of God. Later came the Gnostics and their extra Gospels and "hidden knowledge" they claimed were needful for understanding the Scriptures. Montanists claimed special, necessary insights, inspiration and leadership for following Christ beyond that provided by the Scriptures.

Over the centuries following, a variety of groups of professing believers have carefully drafted statements of belief called "creeds" or "confessions" that have been used to try to guide or test one's understanding of the Word of God. Verbal disputes and physical conflicts, even to bloodshed, have arisen in defense of these creeds or confessions as religious people began to accord to them more and more authority. Mohamadism, (Islam), capitalized upon this tendency and insisted upon adding its own set of instruction to that of Moses, the Prophets, Jesus and His Apostles, daring to add on the teachings of Mohamad to the Word of God.

And who can count the papal bulls that stem from Roman Catholicism's claims that her Pope is Christ's direct representative on earth, given for the proper interpretation of Christ's will? The various Inquisitions were brought to mature form in the Spanish Inquisition in which the creeds of Roman Catholicism were enforced by the civil authorities to the point of torture and bloodshed and deaths (there are some interesting things said to be found in the basements of some ancient Spanish cathedrals).

The Reformation period was not without verbal and physical violence & bloodshed over extra-biblical creeds & confessions from competing factions of people, each professing faith in Christ. Later history records the claims of Mormons with their own extra-biblical writings, (the golden plates, Book of Mormon, etc.) that they teach are necessary to proper understanding of the Word of God. Seventh Day Adventism clings to the writings of Ellen G. White in addition to the Bible. The Jehovah's Witnesses & Watchtower Society claim that the Bible cannot be properly understood without their publications. And who can give a complete accounting for all the denominational conflicts and their strifes between creeds, confessions, doctinal statements, etc.?

What do all these groups have in common? They all produce and hold out writings besides the Word of God, (the Bible), as necessary for correctly understanding the will of God. And they all employ their extra-biblical writings to divide the body of believers in Christ whether inside or outside of the boundaries of their group. They erroneously promote their private interpretations, teaching that the "traditions" of 2 Thessalonians 2:14-15 are something they offer in addition to the New Testament writings. And strife has often followed.

But what did Jesus say? Who is Jesus? He is the Word of God in Person! The Prince of Peace! The only begotten Son of the God of Peace who brought the Gospel of Peace, the walking, talking Bible man Himself, Jesus! Jesus is the Alpha and Omega, the First and Last Letter, the First and Last Word about all orthodoxy, the Beginning and the End about all correct teaching. And the Spirit of God accompanies the Word of God, the Bible. And who are the Apostles, the ones Jesus hand-selected and sent? They are the very authors through whom the Spirit of Christ moved to write the New Testament, the very ones Jesus personally sent out to disciple the nations saying, "Whoever receives you receives Me." And all Christendom peacefully rallies around Him, the Word of God Himself, Jesus Christ the Righteous.

This is not to say that there is no room for comparing notes with fellow believers (by way of creeds) as an aid, as "training wheels," toward a proper understanding of the Word of God. But the ultimate decider of Truth and orthodoxy and correct belief is the Word of God Himself, Jesus Christ. And the Bible is the Word of God.

Jeremiah 2:13
13 For my people have committed two evils; they have forsaken me the fountain of living waters, and hewed them out cisterns, broken cisterns, that can hold no water.

Cisterns serve a good purpose, but they are no substitute for the fountain of fresh water. This is because cisterns leak and cisterns hold water that was collected long ago, stagnant water. Creeds can serve a good purpose, just so long as we recognise them for what they are: cisterns and not the Fountain of Living Water, which is the Word of God. No creed has ever been recognised by the Church as the Word of God. But the Bible is the Word of God. And the Holy Spirit is the Bible's interpreter and He is given to those who obey the Word of God.

Simply put, it is ridiculous to condemn as a heretic someone who:

1. confesses that Jesus the Son of God, (1 John 4:15);
2. believes Jesus is the Christ, (1 John 5:1);
3. confesses that Jesus Christ is the Word of God who came in the flesh, (John 1:1, 14 & 1 John 4:2);
4. confesses the name of Jesus before men, (Matt 10:32);
5. confesses Jesus is Lord while believing in his heart that God raised Jesus from the dead, (Romans 10:9);
6. worships God the Father of our Lord Jesus Christ, (1 John 2:23);
7. abides in the doctrine of Christ, (2 John 9);
8. displays the fruit of the Spirit, (Gal 5:22-24);
9. obeys the Gospel of Paul, (Rom 2:16 & Rom 16:25);
10. values the Old Testament for godly instruction, (2 Tim 3:15-17);
11. loves all the saints & brethren, maintaining good standing & fellowship among the churches, (Eph 1:15 & Col 1:4 & 1 John 3:14);
12. yet understands God & Jesus to be present among us now judging the living and the dead among us now rather than at a time yet future. Wittingly or not, much of global, historic Christianity tacitly testifies agreement to this position by their widespread, ancient & deeply-rooted belief that the Saints of old, (bygone Christians), have been glorified are now present among us for our protection and welfare, "reigning" over the affairs of men from the invisible realm, as declared by the confession, "We believe in the Communion of the Saints," LINK.

Romans 8:33-34
Who shall bring a charge against God's elect? It is God who justifies. 34 Who is he who condemns? It is Christ who died, and furthermore is also risen, who is even at the right hand of God, who also makes intercession for us.
NKJV

Let us always go to Jesus.

John 7:37-39
37 In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink.
38 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.
39 But this spake he of the Spirit, which they that believe on him should receive.

John 1:1-5 & John 1:12-14
In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God. 3 All things were made through Him, and without Him nothing was made that was made. 4 In Him was life, and the life was the light of men. 5 And the light shines in the darkness, and the darkness did not comprehend it.
12 As many as received Him, to them He gave the right to become children of God, to those who believe in His name: 13 who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
14 And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth.
NKJV

Matthew 17:5-6
While he was still speaking, behold, a bright cloud overshadowed them; and suddenly a voice came out of the cloud, saying, "This is My beloved Son, in whom I am well pleased. Hear Him!"
NKJV

1 John 2:26-29
These things I have written to you concerning those who try to deceive you. 27 But the anointing which you have received from Him abides in you, and you do not need that anyone teach you; but as the same anointing teaches you concerning all things, and is true, and is not a lie, and just as it has taught you, you will abide in Him.
28 And now, little children, abide in Him, that when He appears, we may have confidence and not be ashamed before Him at His coming. 29 If you know that He is righteous, you know that everyone who practices righteousness is born of Him.
NKJV

Hebrews 8:10-11
For this is the covenant that I will make with the house of Israel after those days, saith the Lord; I will put my laws into their mind, and write them in their hearts: and I will be to them a God, and they shall be to me a people: 11 And they shall not teach every man his neighbour, and every man his brother, saying, Know the Lord: for all shall know me, from the least to the greatest.

Matthew 23:8-14
But you, do not be called 'Rabbi'; for One is your Teacher, the Christ, and you are all brethren. 9 Do not call anyone on earth your father; for One is your Father, He who is in heaven. 10 And do not be called teachers; for One is your Teacher, the Christ. 11 But he who is greatest among you shall be your servant. 12 And whoever exalts himself will be humbled, and he who humbles himself will be exalted.
13 "But woe to you, scribes and Pharisees, hypocrites! For you shut up the kingdom of heaven against men; for you neither go in yourselves, nor do you allow those who are entering to go in.
NKJV

John 6:63-65
It is the Spirit who gives life; the flesh profits nothing. The words that I speak to you are spirit, and they are life. 64 But there are some of you who do not believe." For Jesus knew from the beginning who they were who did not believe, and who would betray Him. 65 And He said, "Therefore I have said to you that no one can come to Me unless it has been granted to him by My Father."
NKJV

John 6:43-45
Jesus therefore answered and said to them, "Do not murmur among yourselves. 44 No one can come to Me unless the Father who sent Me draws him; and I will raise him up at the last day. 45 It is written in the prophets, 'And they shall all be taught by God.' Therefore everyone who has heard and learned from the Father comes to Me.
NKJV

Matthew 11:27-28 and Luke 10:22
All things have been delivered to Me by My Father, and no one knows the Son except the Father. Nor does anyone know the Father except the Son, and the one to whom the Son wills to reveal Him. 28 Come to Me, all
NKJV

John 14:15-27
15 "If you love Me, keep My commandments. 16 And I will pray the Father, and He will give you another Helper, that He may abide with you forever — 17 the Spirit of truth, whom the world cannot receive, because it neither sees Him nor knows Him; but you know Him, for He dwells with you and will be in you. 18 I will not leave you orphans; I will come to you.
19 "A little while longer and the world will see Me no more, but you will see Me. Because I live, you will live also. 20 At that day you will know that I am in My Father, and you in Me, and I in you. 21 He who has My commandments and keeps them, it is he who loves Me. And he who loves Me will be loved by My Father, and I will love him and manifest Myself to him."
22 Judas (not Iscariot) said to Him, "Lord, how is it that You will manifest Yourself to us, and not to the world?"
23 Jesus answered and said to him, "If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our home with him. 24 He who does not love Me does not keep My words; and the word which you hear is not Mine but the Father's who sent Me.
25 "These things I have spoken to you while being present with you. 26 But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you.
NKJV

Matthew 15:1-9
Then the scribes and Pharisees who were from Jerusalem came to Jesus, saying, 2 "Why do Your disciples transgress the tradition of the elders? For they do not wash their hands when they eat bread."
3 He answered and said to them, "Why do you also transgress the commandment of God because of your tradition? 4 For God commanded, saying, 'Honor your father and your mother'; and, 'He who curses father or mother, let him be put to death.' 5 But you say, 'Whoever says to his father or mother,"Whatever profit you might have received from me is a gift to God" — 6 then he need not honor his father or mother.' Thus you have made the commandment of God of no effect by your tradition. 7 Hypocrites! Well did Isaiah prophesy about you, saying:
8 "These people draw near to Me with their mouth,
And honor Me with their lips,
But their heart is far from Me.
9 And in vain they worship Me,
Teaching as doctrines the commandments of men.'"
NKJV

Mark 7:6-13
He answered and said to them, "Well did Isaiah prophesy of you hypocrites, as it is written:
'This people honors Me with their lips,
But their heart is far from Me.
7 And in vain they worship Me,
Teaching as doctrines the commandments of men.'
8 For laying aside the commandment of God, you hold the tradition of men — the washing of pitchers and cups, and many other such things you do."
9 He said to them, "All too well you reject the commandment of God, that you may keep your tradition. 10 For Moses said, 'Honor your father and your mother'; and, 'He who curses father or mother, let him be put to death.' 11 But you say, 'If a man says to his father or mother,"Whatever profit you might have received from me is Corban" — ' (that is, a gift to God), 12 then you no longer let him do anything for his father or his mother, 13 making the word of God of no effect through your tradition which you have handed down. And many such things you do."
NKJV

1 Timothy 6:2-5
These things teach and exhort.
3 If any man teach otherwise, and consent not to wholesome words, even the words of our Lord Jesus Christ, and to the doctrine which is according to godliness;
4 He is proud, knowing nothing, but doting about questions and strifes of words, whereof cometh envy, strife, railings, evil surmisings,
5 Perverse disputings of men of corrupt minds, and destitute of the truth, supposing that gain is godliness: from such withdraw thyself.

Titus 1:13-2:1
Therefore rebuke them sharply, that they may be sound in the faith, 14 not giving heed to Jewish fables and commandments of men who turn from the truth. 15 To the pure all things are pure, but to those who are defiled and unbelieving nothing is pure; but even their mind and conscience are defiled. 16 They profess to know God, but in works they deny Him, being abominable, disobedient, and disqualified for every good work.
2 But as for you, speak the things which are proper for sound doctrine
NKJV

Galatians 1:6-12
6 I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel:
7 Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.
8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
9 As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed.
10 For do I now persuade men, or God? or do I seek to please men? for if I yet pleased men, I should not be the servant of Christ.
11 But I certify you, brethren, that the gospel which was preached of me is not after man.
12 For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ.

2 Thessalonians 2:13-17
13 But we are bound to give thanks alway to God for you, brethren beloved of the Lord, because God hath from the beginning chosen you to salvation through sanctification of the Spirit and belief of the truth:
14 Whereunto he called you by our gospel, to the obtaining of the glory of our Lord Jesus Christ.
15 Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.
16 Now our Lord Jesus Christ himself, and God, even our Father, which hath loved us, and hath given us everlasting consolation and good hope through grace,
17 Comfort your hearts, and stablish you in every good word and work.

Proverbs 30:5-6
Every word of God is pure;
He is a shield to those who put their trust in Him.
6 Do not add to His words,
Lest He rebuke you, and you be found a liar.
NKJV

Deuteronomy 12:32
"Whatever I command you, be careful to observe it; you shall not add to it nor take away from it.
NKJV

Deuteronomy 4:2-3
You shall not add to the word which I command you, nor take from it, that you may keep the commandments of the Lord your God which I command you.
NKJV

1 John 3:9-14
Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.
10 In this the children of God and the children of the devil are manifest: Whoever does not practice righteousness is not of God, nor is he who does not love his brother. 11 For this is the message that you heard from the beginning, that we should love one another, 12 not as Cain who was of the wicked one and murdered his brother. And why did he murder him? Because his works were evil and his brother's righteous.
13 Do not marvel, my brethren, if the world hates you. 14 We know that we have passed from death to life, because we love the brethren.
NKJV

John 13:20 Verily, verily, I say unto you, He that receiveth whomsoever I send receiveth me; and he that receiveth me receiveth him that sent me.

John 20:19-22
Then were the disciples glad, when they saw the Lord.21 Then said Jesus to them again, Peace be unto you: as my Father hath sent me, even so send I you.22 And when he had said this, he breathed on them, and saith unto them, Receive ye the Holy Ghost:

1 Peter 1:12
unto us they did minister the things, which are now reported unto you by them that have preached the gospel unto you with the Holy Ghost sent down from heaven

2 Corinthians 11:12-21
I will keep on doing what I am doing in order to cut the ground from under those who want an opportunity to be considered equal with us in the things they boast about.
13 For such men are false apostles, deceitful workmen, masquerading as apostles of Christ. 14 And no wonder, for Satan himself masquerades as an angel of light. 15 It is not surprising, then, if his servants masquerade as servants of righteousness. Their end will be what their actions deserve.
16 I repeat: Let no one take me for a fool. But if you do, then receive me just as you would a fool, so that I may do a little boasting. 17 In this self-confident boasting I am not talking as the Lord would, but as a fool. 18 Since many are boasting in the way the world does, I too will boast. 19 You gladly put up with fools since you are so wise! 20 In fact, you even put up with anyone who enslaves you or exploits you or takes advantage of you or pushes himself forward or slaps you in the face.
NIV

1 John 4:2-17 through 1 John 5:1-20
2 By this you know the Spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is of God, 3 and every spirit that does not confess that Jesus Christ has come in the flesh is not of God. And this is the spirit of the Antichrist, which you have heard was coming, and is now already in the world.
4 You are of God, little children, and have overcome them, because He who is in you is greater than he who is in the world. 5 They are of the world. Therefore they speak as of the world, and the world hears them. 6 We are of God. He who knows God hears us; he who is not of God does not hear us. By this we know the spirit of truth and the spirit of error.
7 Beloved, let us love one another, for love is of God; and everyone who loves is born of God and knows God. 8 He who does not love does not know God, for God is love. 9 In this the love of God was manifested toward us, that God has sent His only begotten Son into the world, that we might live through Him. 10 In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins. 11 Beloved, if God so loved us, we also ought to love one another.
12 No one has seen God at any time. If we love one another, God abides in us, and His love has been perfected in us. 13 By this we know that we abide in Him, and He in us, because He has given us of His Spirit. 14 And we have seen and testify that the Father has sent the Son as Savior of the world. 15 Whoever confesses that Jesus is the Son of God, God abides in him, and he in God. 16 And we have known and believed the love that God has for us. God is love, and he who abides in love abides in God, and God in him.

5:1 Whoever believes that Jesus is the Christ is born of God, and everyone who loves Him who begot also loves him who is begotten of Him. 2 By this we know that we love the children of God, when we love God and keep His commandments. 3 For this is the love of God, that we keep His commandments. And His commandments are not burdensome. 4 For whatever is born of God overcomes the world. And this is the victory that has overcome the world — our faith. 5 Who is he who overcomes the world, but he who believes that Jesus is the Son of God?
6 This is He who came by water and blood — Jesus Christ; not only by water, but by water and blood. And it is the Spirit who bears witness, because the Spirit is truth. 7 For there are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one. 8 And there are three that bear witness on earth: the Spirit, the water, and the blood; and these three agree as one.

9 If we receive the witness of men, the witness of God is greater; for this is the witness of God which He has testified of His Son. 10 He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son. 11 And this is the testimony: that God has given us eternal life, and this life is in His Son. 12 He who has the Son has life; he who does not have the Son of God does not have life. 13 These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life, and that you may continue to believe in the name of the Son of God.

14 Now this is the confidence that we have in Him, that if we ask anything according to His will, He hears us. 15 And if we know that He hears us, whatever we ask, we know that we have the petitions that we have asked of Him.
16 If anyone sees his brother sinning a sin which does not lead to death, he will ask, and He will give him life for those who commit sin not leading to death. There is sin leading to death. I do not say that he should pray about that. 17 All unrighteousness is sin, and there is sin not leading to death.
18 We know that whoever is born of God does not sin; but he who has been born of God keeps himself, and the wicked one does not touch him.
19 We know that we are of God, and the whole world lies under the sway of the wicked one.
20 And we know that the Son of God has come and has given us an understanding, that we may know Him who is true; and we are in Him who is true, in His Son Jesus Christ. This is the true God and eternal life.
21 Little children, keep yourselves from idols. Amen.
NKJV

John 15:9-15
9 "As the Father loved Me, I also have loved you; abide in My love. 10 If you keep My commandments, you will abide in My love, just as I have kept My Father's commandments and abide in His love.
11 "These things I have spoken to you, that My joy may remain in you, and that your joy may be full. 12 This is My commandment, that you love one another as I have loved you. 13 Greater love has no one than this, than to lay down one's life for his friends. 14 You are My friends if you do whatever I command you.
NKJV

John 20:28-31
28 And Thomas answered and said to Him, "My Lord and my God!"
29 Jesus said to him, "Thomas, because you have seen Me, you have believed. Blessed are those who have not seen and yet have believed."
30 And truly Jesus did many other signs in the presence of His disciples, which are not written in this book; 31 but these are written that you may believe that Jesus is the Christ, the Son of God, and that believing you may have life in His name.
NKJV

John 1:1-5 & John 1:12-14
In the beginning was the Word, and the Word was with God, and the Word was God. 2 He was in the beginning with God. 3 All things were made through Him, and without Him nothing was made that was made. 4 In Him was life, and the life was the light of men. 5 And the light shines in the darkness, and the darkness did not comprehend it.
12 As many as received Him, to them He gave the right to become children of God, to those who believe in His name: 13 who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
14 And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth.
NKJV

Romans 10:8-13
But what does it say? "The Word is near you; it is in your mouth and in your heart," that is, the Word of faith we are proclaiming: 9 That if you confess with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved. 10 For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved. 11 As the Scripture says, "Anyone who trusts in him will never be put to shame." 12 For there is no difference between Jew and Gentile — the same Lord is Lord of all and richly blesses all who call on him, 13 for, "Everyone who calls on the name of the Lord will be saved."
NIV

Hebrews 13:8
Jesus Christ the same yesterday, and to day, and for ever.

Matthew 24:35 Mark 13:31 Luke 21:33
"Heaven and earth shall pass away, but My words shall not pass away."