In Greek New Testament, Nestle, and Good News Translation, this verse is taken as part of verse 6. In And the Spirit is the witness, the discourse turns now to the Spirit. This may seem a rather abrupt shift, but it was not so for John. In his school of thought there must have been a close connection between the Divine Sonship and the Spirit, as is shown, for example, by John 1.32-33; 3.34. For the Spirit (in the sense of God’s Spirit, or the Holy Spirit) see comments on 4.1.

The witness in the Greek is a participle of the present tense, literally “the witnessing/testifying one”; see comments on “to testify” in 1.2. The present tense expresses continuation. The reference is to the continuing witness, or testimony, of the Spirit in the congregation (compare also John 14.26 and 15.26). The verb is used here in the sense of “to affirm,” “to assert as valid,” “to say that something (here Jesus’ coming by water and blood) has really happened as stated.”

In order to stress that the Spirit’s testimony about the circumstances of Jesus’ coming can be trusted, the author adds because the Spirit is the truth, that is, because all which the Spirit does or says has the quality of divine truth. Sometimes the absoluteness of this assertion can be better brought out by a negative wording such as ‘because the Spirit cannot be a lie (or a liar).’ For truth see also comments on 1.8.

Quoted with permission from Haas, C., de Jonge, M. and Swellengrebel, J.L. A Handbook on The First Letter of John. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .