The earliest New Testament manuscripts made no mention of a trinity. Here's Bishop Clement of Alexandria [1] in 200 AD quoting from the First Epistle of St. John: "Because there are three who testify, the spirit, and the water, and the blood: and these three are one." Three things are mentioned above, but there's no mention of a three-in-one god, the "trinity". Nor is any trinity, or anything like it, discussed in any of the New Testament manuscripts before about 600 CE, including the Latin and Greek translations. As will be seen, an addition was made to John's verse later.

A Trinity Finally Appeared After Several Centuries

After two centuries of extensive disputes about trinity doctrine, somebody apparently decided to remove the first comma after "testify" in the verses above and replace it with the words, "in heaven: Father, Word and Holy Spirit; and these three are one; and there are three who testify on earth:"  This late addition appeared only in two Latin translations of the Bible, the Old Latin, and Vulgate bible. It is not our job here to explain who did this, or why they did it, but to show evidence that it happened.

The Trinity Is Inserted into John's First Epistle

The words italics in the added verse below (and shown above) represent what is called the "Comma", (a short addition, or clause) or, the "Johannine Comma":  

"Because there are three who testify in heaven: Father, Word and Holy Spirit; and these three are one; and there are three who testify on earth: the Spirit and the water and the blood; and these three are one." (1 John 5:7-8 KJV).

Evidence Against the Trinity Verse

There are three main reasons for believing that the trinity verse is a late addition; we discuss these reasons below:

Virtually No Biblical Corroboration

As support for a doctrine as important as the Trinitarian, one would expect ample discussion in the New Testament. But, nowhere else in 1 John is the Holy Spirit or the Word mentioned. Nowhere in the entire New Testament is there mentioned a single entity composed of the Father, the Word, and the Holy Spirit. In the much-disputed Matthew passage urging his followers to "go ye therefore and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost" (Matthew 28:19), the three divine entities are mentioned as individual entities, but not even in this disputed passage does it say they are "one". (Evidence that Matthew 28:19 is a fraud is given in the essay Did Jesus Reach Out to the Gentiles?)

The Greeks Didn't Believe It

During the twelve hundred years between Bishop Clement's first mention of John's gospel in about 200 AD, until about 1500 AD, there appeared five thousand Greek manuscripts of the New Testament, but only eight contain the comma, and these eight appeared only after 1400 AD, thirteen hundred years after the Bible writers had finished their work.

The Church Doubted It -- But Kept Quiet

"The famous passage of the Three Witnesses is found in none of the ancient manuscripts. [Other] facts... militate against the canonicity of the Three Witnesses. However, the Catholic theologian must take into account more than textual criticism." (Catholic Encyclopedia, viii, 436, published under the Imprimatur of Archbishop Farley; New York, Robert Appleton Co., 1907-1909.)

The church is thus confessing that there is good reason to suspect the trinity verses. But note: the church, also said, in effect, that church doctrine took precedent over the truth. It thus apparently acquiesced in a fraud in order to preserve the only testimony for a Trinity. So much for a church whose popes had declared, "never deceives and never errs, and shall never err to all eternity."

Other Bible Versions Omit Trinity Verse

For there are three that testify: [i] the Spirit and the water and the blood; and the three are in agreement.(1 John 5:7-8 NASB), see footnote [i] below.) For there are three that testify: [ii] the Spirit, the water and the blood; and the three are in agreement. (1 John 5:7-8 NIV, see footnote [ii] below.)  And the Spirit is the witness, because the Spirit is the truth. There are three witnesses, the Spirit, the water, and the blood; and these three agree. (1 John 5:7-8 RSV)

Biblical Footnotes Rejecting Trinity Verse

[i] A few late manuscripts add ... "in heaven, the Father, the Word, and the Holy Spirit, and these three are one. And there are three that testify on earth, the Spirit".

[ii] Late manuscripts of the Vulgate: "in heaven: the Father, the Word and the Holy Spirit, and these three are one. And there are three that testify on earth:" (not found in any Greek manuscript before the sixteenth century.)

Naive bible-believers often mistake footnotes in their Bibles as accepted alternative translations, endorsed by the editors of that version; this is far from the truth. The footnotes above are evidence that the editors of the New American Standard Bible and New International Version recognize that the Comma is fraudulent, and not worthy of being in their Bible. In support of our comments above, these editors note that the Comma appears only in "later manuscripts", which means they accept the notion that the comma was added long after the inspired writers of the Bible had completed their work.

King James Bible Accepts Trinity Verse

On January 13, 1897, the Sacred Congregation of the Inquisition in Rome issued a declaration (confirmed by Pope Leo XIII on January 15) that one could not safely deny or call into doubt the authenticity of the Comma. But long before this in 1611, for reasons which we will not discuss here, the editors of the King James Version of the Bible chose one of the very few, and very late, Greek translations containing the false verse. Thus, we have today the complete--and fraudulent--trinity verse as repeated in the King James Bible:  "For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one." (1 John 5:7-8 KJV)

If it is true that the trinity verse is fraudulent, then the King James Bible is partially in error. The author has derived much of this information from the works of others. [3,4]

 A couple of readers dispute the author contention that there is no verse which unmistakably says that the three divine entities are one; this is discussed in the appendix.

[1] Clement Alexandria, Fragment from Cassiodorous, Ch. 3; ANF iii, 576. Ante-Nicene Fathers is a collection of the extant writings of all the founders of Christianity down to the council of Nicaea, of Nice, in 325 AD.

Ante-Nicene literature was that written prior to the Council of Nicaea, which was called by Constantine in 325 to settle disputed religious doctrines. The first of these works were written by the Apostolic Fathers of the 1st and early 2nd centuries.

In the 2nd century another group of writers, the apologists, defended Christianity against its persecutors and against other religious beliefs. Among the apologists were St. Justin Martyr, St. Irenaeus, St. Clement of Alexandria, and others. (Ref: "Compton's Living Encylcopedia")
[2] Anchor Bible, New Test., v. 30, The Epistles of John, by Raymond E. Brown, S.S. (New York: Doubleday and Co., 1982) Brown notes that all recent Catholic scholarly discussion has recognized that the Comma is neither genuine nor authentic.
[3] Cheating with the Text--The Johannine Comma, Larry Taylor.
[4] Forgery In Christianity, Joseph Wheless (1930), p 192-194.
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Appendix

The verses below are often offered as evidence that the Bible writers were aware of the trinity:

"John to the seven churches which are in Asia: Grace be unto you, and peace, from him [God] which is, and which was, and which is to come; and from the seven Spirits which are before his throne; And from Jesus Christ, who is the faithful witness, and the first begotten of the dead, and the prince of the kings of the earth." (Revelation 1:4-5)

The Revelation verse above is three references to three separate entities: the seven spirits of the seven churches, God, and Jesus Christ. There is no evidence that John means for us to believe that he thinks these entities represent three manifestations of the same god.

"The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Ghost, be with you all." (2 Corinthians 13:14)

This says nothing about Jesus, God, and Holy Ghost being one in the same God; just mentioning the three entities in the same verse does not show that the writer meant for the reader to know that they were one God.

There are several verses identifying God with the Holy Spirit.

"Cast me not away from thy presence; and take not thy holy spirit from me. (Psalms 51:11).....But they rebelled, and vexed his holy Spirit: therefore he was turned to be their enemy, and he fought against them. (Isaiah 63:10)....Then he remembered the days of old, Moses, and his people, saying,Where is he that brought them up out of the sea with the shepherd of his flock? where is he that put his holy Spirit within him? (Isaiah 63:11)....If ye then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him? (Luke 11:13)....In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise (Ephesians 1:13)...And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption. (Ephesans 4:30) ...He therefore that despiseth, despiseth not man, but God, who hath also given unto us his holy Spirit." (1 Thessalonians 4:8)

These references to the Holy Spirit do not suggest that this is one of the three gods of the trinity; the repeated use of the phrase "his holy Spirit" suggest that the writer is talking about an attribute of God, not a separate manifestation of God. Other verses above speak of giving the Holy Spirit to someone (not something you'd do with a God).

Innumerable verses show that Jesus was one with God, but that falls one short of proclaiming a trinity of gods.