Textual evidence may be cited (cf. p. 10) for the reading “do his commandments.” The variation makes little difference to the writer’s ultimate meaning. See on v. 3.
When we love God.
John clearly teaches that love for God is basic in the Christian’s experience. He who loves God may be sure of also loving his brethren. It is therefore of paramount importance for the believer to cultivate a genuine love for his Maker: it will prove an inexhaustible fount from which all other desirable qualities will ceaselessly flow. It will also control his other affections, keeping them pure and well proportioned, contributing to the development of symmetrical Christian character.
See on ch. 2:3, 29. We have been told how we may know that we love God (ch. 4:20, 21), and now John tells us how to discover whether we do or do not love the children of God, who are our brothers.