Question

Answer

While the doctrine of the Trinity is clearly taught throughout the Bible as a whole, this particular verse is almost certainly a later insertion, perhaps by Jermone as he published his Latin version of the Bible. None of the earliest Greek manuscripts of 1 John that we have contain the bulk of this verse and some of verse 8.

Some older translations of the Bible use a set of manuscripts which are not as ancient as the ones we have now. For instance, since the publication of the King James Version in 1611, more ancient manuscripts of the New Testament have been discovered. And those more ancient manuscripts don't have the words in question, so new translations of the Bible tend to leave it them out.