My question is: Why is 1 John 5:7 which is in the KJV not included in most other translations?
It’s because the underlined part of 1 John 5:7-8 which reads, “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” in the KJV is in doubt.
Those opposed to its inclusion point out that it cannot be found in any Greek manuscripts prior to the 16th century, and as far as we can tell was not quoted by the early Church fathers. They say the King James version of 1 John 5:7-8 was taken from the Latin Vulgate rather than the “more reliable” Greek translations and was used under pressure from the Catholic Church.
Those who want it included claim that early transcribers, influenced by Gnosticism, deleted this and other references to the Trinity out of many Greek texts and that’s why modern translations who rely on these “mutilated” texts don’t have it. In any case the total wordage as given in the KJV can’t be found in any Bible translations earlier than 1522 or later than 1900.
It’s fascinating that there’s no theological argument with the KJV version. The only dispute is over whether John wrote it that way or not. I guess we’ll just have to wait till we can ask him in person to find out.