Every one who believes that Jesus is the Christ is a child of God: the clause resembles verse 4.7, but there the proof that a person is born of God is brotherly love, while here it is faith. Since the theme of faith is not continued, however, the reference seems to be merely an anticipation of what will be said in verses 5-10.

For “to believe” see comments on 3.23, for the Christ see comments on 2.22, and for is a child of God (in the Greek literally “is begotten out of God”) see comments on “is born of him” in 2.29.

Every one who loves the parent loves the child: the preceding sentence, verse 1a, referred to a basic reality of Christian life: the believer is a child of God, or, stated otherwise, the believer has God as his Father. The present sentence, verse 1b, refers to a general rule of human family life: every man who loves a father loves that father’s children. Seen in connection with verse 1a, however, a slightly more specific meaning of this sentence suggests itself to the reader, namely, every man who loves his father loves also his father’s children, that is, his own brothers and sisters. As such the sentence leads up to verse 2, which deals with the relationship between brotherly love and the love for God.

In this context the indefinite pronoun every one is sometimes better rendered by the first person plural pronoun (inclusive); for example, ‘if we love our father thus, we also love our brothers.’

For the parent the Greek has literally “the one-who-begets.” If the relationship has to be specific, one may say ‘he who begat him,’ ‘the one who caused him to be born,’ ‘his father.’

For the child the Greek has literally “the-one-who is-begotten out of him” (the pronoun referring back to “the one-who-begets”). Other possible renderings are ‘the one he begat,’ ‘the one he has caused-to-be-born,’ ‘that one’s child,’ or quite explicitly ‘every other child of that father.’

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 .