“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.”

If John had written these words, they would be the only explicit reference to the Trinity in the Bible. Thankfully, the doctrine of the Trinity doesn’t depend on this passage! Even though modern translations put these words in the footnotes, there are many passages in our Bible that lay the groundwork for the doctrine of the Trinity. But these words here are not original, and it is better to base doctrine on words that we know were written by the New Testament authors.

Here are seven points that summarize why we don’t consider this verse to be the original text.

1. The words occur in only eight late Greek manuscripts: four in the text, and four listed as variant readings. This means every Greek manuscript until the 14th century lacks the words (except for a variant reading in a 10th century manuscript).
2. They are not quoted by any of the early Greek Fathers until the fifth century, who would have certainly used them in their defense of the Trinity if the words were authentic.
3. The words are absent from all ancient translations (Syriac, Coptic, Armenian, Ethiopic, Arabic, Slavonic) except Latin.
4. They are not present in the Old Latin used by Tertullian, Cyprian, or Augustine.
5. They are not in Jerome’s Latin Vulgate but were added to the Vulgate in the ninth century.
6. The words first appear in a fourth century Latin treatise, Liber apologeticus.
7. The Comma Johanneum was not in Erasmus’ first or second edition of his Greek text, what eventually came to be called Textus Receptus.

How did these words get into the Bible? Erasmus states that they were not original, but due to church pressure he added them from a suspected forged Greek manuscript (minuscule 61, Codex Montfortianus.) in his third edition of the Greek New Testament. And this edition was essentially the basis for the KJV.

Bruce Metzger recounts the story behind the forgery. Erasmus did not include the words because he could find no Greek manuscript with the words, but he felt the pressure to insert the Comma Johanneum “in future editions if a single Greek manuscript could be found that contained the passage. At length such a copy was found—or was made to order! As it now appears, the Greek manuscript had probably been written in Oxford about 1520 by a Franciscan friar named Froy (or Roy), who took the disputed words from the Latin Vulgate. Erasmus inserted the passage in his third edition (1522), but in a lengthy footnote that was included in his volume of annotations, he intimated his suspicion that the manuscript had been prepared expressly in order to confute him” (Bruce Metzger and Bart Ehrman, The Text of the New Testament. Its Transmission, Corruption, and Restoration, 4th ed [Oxford, 2005] 146–47).

Why even include these words as a footnote? Most modern translations include them out of respect for the tradition of the King James. A lot of angry words have been spilt over this passage in the blogosphere, but I would add that if it is wrong to drop out words from the Bible, it is equally as wrong to add them (Rev 22:18–19).