Why is 1 John 5:7–8 omitted from almost all all modern translations of the Bible? Is it because the doctrine of the trinity is an invention of the modern church, inserted hundreds of years after the death of the author.

 

This verse could be considered controversial when examining it solely through the lens of manuscripts, as Erasmus did for example.

It's worth noting that much of today's scholarship often overlooks the writings and citations of our Church Father’s. While it's not definitive, we can reasonably assert the originality of this verse, dating back far earlier than the 12th/16th century, based on citations of our Church Father's.

Cyprian of Carthage, an early Church Father, cited this verse in 258 AD (Pre-Nicea) and Jerome included it in his Latin Vulgate too. In Cyprian's work’s “On the Unity of the Church - Chapter 6”, he clearly states:

“and again it is written of the Father, and of the Son and of the Holy Spirit, And these three are one. 1 John 5:7”. This establishes its existence as early as 258 AD. Not only does he cite the verse, he also states that it's written. (Meaning it obviously existed on Greek manuscripts).

I'd also like to add that a heretical Christian sect known as the “Arians”, were very influential in the early Church (before their refutation of their doctrine at Nicea), who had biases against the Trinity and had control over the majority Greek Manuscripts. Given that this verse overtly supports the Trinity, (which is contrary to their beliefs), it was likely removed from the majority manuscripts by them.

Jerome of Stridon and Cyprian of Carthage defended this verse from the Arians, to establish it’s originality. I believe the Church Fathers remained faithful in their attempt to defend God's Word.

As for its omittance, the verse is still there in many modern translations. Though instead of “Father, Son and Spirit” it says “Blood, water and Spirit”. Only the KJV and NKJV includes the Johannine Comma. It's probably omitted due to it’s controversy.