For By this we know (or “By this we are sure”), compare comments on 2.3. By this is probably best taken as pointing back towards the general rule given in verse 1b; then the phrase introduces the conclusion to be drawn from that rule.
The next two clauses may be rendered ‘we love the children of God whenever we love God and obey his commandments’ or, transposing the clauses, ‘whenever we love God and observe his commandments, we must also love his children.’ In the latter rendering the clause sequence of verse 2 parallels that of verse 1b, which may help the reader to make the right connection between the two.
We love: the Greek form is to be taken as an indicative, stating a fact with the force of an obligation; hence ‘we must love.’
For the children of God see comments on 3.1.
When: the Greek conjunction occurs here with the following subjunctive of the present tense. This construction is used when the event of the subordinate clause occurs at the same time as that of the main clause. It usually indicates repeated action; hence when means ‘whenever,’ ‘as often as,’ ‘every time that.’
Obey his commandments, is literally “do his commandments.” Other possible renderings are ‘act according to his commandments,’ ‘do as he commands,’ ‘do what he commands us (to do).’
The interpretation of verses 1-2 advocated here is the most probable one in the present authors’ view, but not the only possible one. There are two main alternatives: (1) Verse 1b may refer to the relationship existing between the believer and God the Father, or to that between the believer and other believers (not, however, to that between God the Father and Jesus the Son). (2) The words “by this” in verse 2 may be interpreted as pointing forward to the “when” clause.
An objection against interpretation (2) is that it differs from the usual order of thought in this Letter. It would imply that a man can know whether he loves his fellow men by asking himself whether he loves God and keeps His commandments. John’s usual argument is the other way round. In 3.14, 17-19, for example, he assumes that man’s immediate experience is his love for man, and that from this he derives the assurance of his relation to God.
Other commentators and translators do not think this objection is valid. According to them verse 2 has a different meaning, namely, that love for God is the proof of true love for the brother, which proof is to be found in the strict observance of the commandments; see verse 2a. This interpretation is represented, for example, by Good News Translation.
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 .
