There is a passage in the New Testament that seems to be an extraordinarily clear statement about the Trinity—1Jo 5:7.

For there are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one

This Verse Does Not Belong in Scripture

Although this verse clearly teaches the Trinity, there is serious question as to whether it belongs in Scripture. The evidence for its inclusion in the New Testament is nil. The passage found its way into the King James Version of the Bible by a strange route. Almost every modern translation of Scripture rejects its authority.

It Should Not Be Used to Argue for the Trinity

Consequently this verse should not be used in discussion about the Trinity. There is sufficient evidence in the Scripture with respect to the Trinity without appealing to 1Jo 5:7.

Summary

Although 1Jo 5:7, as it reads in the King James Version, is a clear Trinitarian statement, there does not seem to be much chance that it is original with First John. This verse should not be used in discussions concerning the biblical doctrine of the Trinity. There is sufficient evidence in Scripture for the Trinity without appealing to 1Jo 5:7.