Adam Clarke on 1 John 5:15

And if we know that he hear us - Seeing we are satisfied that he hears the prayer of faith, requesting the things which himself has promised; we know, consequently, that we have the petitions - the answer to the petitions, that we desired of him; for he cannot deny himself; and we may consider them as sure as if we had them; and we shall have them as soon as we plead for and need them. We are not to ask to-day for mercy that we now need, and not receive it till to-morrow, or some future time. God gives it to him who prays, when it is needful.