Let us love one another: the Greek verb is in the present tense, which has perhaps been used to express continuation. The latter is brought out in a rendering like “let us go on loving one another” (Phillips).

In this and the following verses of the section, the pronoun us has inclusive force. For “to love one another” see comments on 3.11.

For love is of God: this clause serves to express that God is the origin or ultimate cause of all feelings and deeds of love; compare comments on “to be of” in 2.16. Some possible renderings are “love comes from God” (Good News Translation) or, where a verb form of ‘to love’ must be used, ‘if we love, it is God who causes us to do so’; compare also ‘it is because of God that we become like ones-who-love,’ as one American Indian language has it.

Such shifts may make unavoidable the mentioning of the goal. The goal to be added then should be ‘God and one another.’

And he who loves … is a new sentence, not dependent upon for in the preceding sentence. If a goal must be added, it should agree with that in the preceding clause.

For is born of God see comments on 2.29 and 3.9.

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 .