1 John 5:7 For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. (KJV)
(The only EXPLICIT verse spelling out the Trinitarian formula.)
Taken from : Theodore H. Mann, “Textual problems in the KJV New Testament”, in: Journal of Biblical Studies 1 (January–March 2001).
When Erasmus compiled his Greek New Testament for Johann Froben in 1515, he neglected to include the above passage. A firestorm of protest erupted, led by a man called Stunica, who had been one of the editors of the Complutensian Polyglot. Latin versions had included it and it was widely accepted as part of the approved New Testament text.
Erasmus responded that he left the passage out because it did not appear in any of the Greek manuscripts available to him, but that he would include it in future editions of his Greek New Testament if a Greek manuscript could be found which contained it.
In time, a manuscript was located, or rather produced. As it turned out, it had been written in Oxford by a Franciscan friar named Froy (perhaps a few others were involved as well), who had back-translated the material from the Latin Vulgate. Erasmus kept his word, however, and included the Comma Johanneum, as it came to be called, in his third edition, but with a note stating that he doubted its authenticity.
Erasmus was, of course, eventually proved right. Out of the thousands of extant Greek New Testament manuscripts, this passage appears in only eight (listed below). As you examine the list, note that the earliest appearance of this reading is a later addition to a 10th-century manuscript (how much later, one wonders), and then only as a variant reading (meaning that it was offered as an alternative reading to the one appearing in the main body of the text). Also note that all of the other seven sources are dated in the same century in which Erasmus lived (16th), or later (18th). Furthermore, four out of the eight (b, c, d and e) are hand-written additions, added to the margins of the documents, and are not part of the texts themselves. To my knowledge, none of the early church Fathers mention it; it appears in none of the early versions. It does not even appear in the Vulgate until around the year 800.
It was, I understand, added to a Latin translation by a friar in the early Middle Ages. It then began to appear, here and there, in other Latin versions, finally becoming incorporated into the body of the biblical text itself, becoming part of the Vulgate, and ultimately finding its way into the English, where it was accepted.
Clearly, this passage was never written by the apostle John.
Manuscripts Containing the Comma Johanneum:
a. #61: Codex Montfortianus, dating from the early 16th century. . This is the manuscript shown to Erasmus to force him to include the Comma Johanneum in his GNT.
b. #88: A variant reading in a 16th-century hand, added to the 14th-century codex Regius of Naples.
c. #221: A variant reading added to a 10th-century manuscript in the Bodleian Library at Oxford.
d. #429: A variant reading added to a 16th-century manuscript at Wolfenbuttel.
e. #636: A variant reading added to a 16th-century manuscript at Naples.
f. #918: A 16th-century manuscript at the Escorial, Spain.
g. #2318: An 18th-century manuscript, influenced by the Clementine Vulgate, at Bucharest, Rumania.
h. #629: 16th Century. Much of this was back-translated from the Vulgate, including a partial quote of the Comma Johanneum. (The phrase, “… and these three are one” is missing.)