After his digression about faith and confession, the author arranges his thoughts to return to his main theme. This verse has therefore the character of a summary of verses 14-15, which in their turn take up verses 9-10.

Greek New Testament, Nestle, and several versions take verse 16b as the beginning of a new paragraph. In the opinion of the present authors, this is not advisable because the repetition of the emphatic formula he … abides in God, and God abides in him (compare verses 13, 15) seems rather to mark the end of the present paragraph. Accordingly the verse is treated as a whole in these notes.

So connects the verse rather loosely with what precedes. It has here the force of “thus we may say that.”

We know and believe the love God has for us: the verbs are both in the perfect tense in the Greek. This gives them the force of “we have come to know and believe and still know and believe.” The second verb reinforces the first.

We … believe the love: the construction of this verb with a direct object is rather uncommon in the Greek. In the Johannine writings it occurs only here and in “Do you believe this” in John 11.26.

The verb believe has already been discussed in the comment on 3.23, which see. It is used here to bring out that we are convinced of the truth of what we came to know, namely, God’s love for us; hence such renderings as “to have put one’s trust in” (Translators’ Translation), ‘to be absolutely/truly sure of,’ ‘to rest the weight of one’s heart on,’ ‘never to doubt.’ In some cases the reinforcing function of “to believe” is expressed otherwise and in another part of the sentence, as in ‘we know, “God truly loves us.” ’

The love God has for us, or ‘that God is loving us’: the verb form has is in the present tense, expressing duration. As to for us (literally “in us”) see comments on “among us” in 1 John 4.9.

For God is love see comments on 1 John 4.8 The statement is repeated here to remind the reader that the source of all love is God; whether we love God or our brothers, it is God’s love that is at work in us.

For he who abides in love, or ‘he who is-and-remains in love,’ ‘he who loves and goes on loving,’ see comments on 2.10. If one has to indicate explicitly who is loved, one may add ‘God and his brother(s).’

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 .