Verses 14-15 serve to assure the reader that God hears (that is, listens and gives heed to) the believers whenever they ask him anything according to his will, and that his hearing them implies his granting them whatever they ask of him in such a way.
This points forward to the that clause. The latter indicates why the Christians have confidence in God. The verse may have to be restructured; for example, ‘the confidence which we have in him is based on the fact that he hears us whenever we ask him anything…,’ ‘this is the reason why we confide in him: whenever we ask him anything … he hears us’; or, changing the clause order, ‘it is a fact that he hears us whenever we ask him anything…; that is why we confide in him.’
The confidence which we have in him: see comments on 2.28 and 3.21. Here and in verses 15, 18-20 the pronoun we has inclusive force. The pronoun him refers to God.
If, or ‘whenever,’ is “expectational” here; see comments on 1.6.
We ask anything, namely, from God: the reference probably is to something that God is asked to do rather than to an object he is requested to grant. For “to ask” in the sense of “to pray,” see comments on 3.22.
According to his will refers to the circumstances under which the proposition holds true. A person may only be sure that his prayer will be heard when he knows and obeys God’s will just as Christ did. Thus his praying means becoming of one mind with God, uniting his will with God’s will and allowing his desires to be redirected according to God’s mind. Some renderings used are ‘ready to do what he wants,’ ‘while our hearts are the same with (that is, we are of the same mind as) God.’ For will see comments on 2.17.
He hears us, or ‘he listens to us,’ ‘he gives attention to us (or to our words),’ ‘he takes-in what we-ask,’ ‘he concerns himself about us.’ In one language the idiomatic expression is ‘he grabs our words.’ The term implies a response. Therefore some renderings used here cover two concepts; for example, ‘to listen’ and ‘to answer,’ or ‘to understand’ and ‘to obey.’
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 .