1 John 1:4

These things. That is, the content of the epistle, including what has already been written in vs. 1-3, and what the author intends to write in the remainder of the letter.

Unto you. Important textual evidence may be cited (cf. p. 10) for omission of this phrase and for reading in its place an emphatic form of the subject of the verb in the Greek. The resultant reading would be “and these things we write.”

Your. Important textual evidence may be cited for the reading “our.” But the context favors the reading of the KJV, since it is more likely that John writes to bring joy to his readers than to himself.

Joy. The natural result of fellowship with Christ (see on Rom. 14:17).

Full. Or, “fulfilled.” Jesus had expressed the same reason for speaking “these things” to His disciples (John 15:11), and the beloved disciple may well be echoing the words of his Master. The fulfillment of joy is a frequent theme in John’s writings (John 3:29; 15:11; 16:24; 17:13; 2 John 12). The Christian religion is a happy one (see on John 15:11).

Thus ends the brief introduction to the epistle. John, who has personally known Christ, desires to share his knowledge with his readers in order that they may enjoy the same fellowship he is already enjoying with the Father and the Son. In the course of expressing this loving desire, he asserts the divinity, the eternity, and the incarnation — and consequent humanity — of the Son. This wondrous knowledge he conveys in simple but emphatic language so that readers, in his own day and in ours, may have no doubt concerning the foundation of the Christian faith and the nature and work of Jesus Christ. In this way he effectively answers Gnostic teaching without even mentioning the heresy.