Theophylact of Ohrid

Then he says that the sign of this undoubted faith is none other than the boldness which we find before Him through blameless faith, as we also said above, and that in turn the sign of such boldness is the obtaining of everything we ask. But since not all receive everything they ask, and not all requests are heard, he adds: "according to His will," that is, whoever asks for something contrary to the will of the Teacher will not be heard either. …

Commentary on 1 John ↗

Oecumenius

And this is the confidence that we have in Him, that if we ask anything according to His will, He hears us. And if we know that He hears us in whatever we ask, we know that we have the requests that we have asked of Him. Then, since there is no other sign of this unquestionable faith except trust, which we find in Him through irreproachable faith, as we have also said before. Again, He has set a sign of this trust, that we are not to be frustrated in all that is asked of us. …

Commentary on 1 John ↗

Clement of Alexandria

"And this is the confidence which we have towards Him, that if we ask anything according to His will, He will hear us." He does not say absolutely what we shall ask, but what we ought to ask.

From the Latin Translation of Cassiodorus ↗

Bede

And this is the confidence that we have toward him, etc. He provides us with great confidence to hope for heavenly goods from the Lord, because even in this life, whatever we ask of him in a salutary manner, we obtain, according to what he himself promises believers in the Gospel: "I say to you, whatever you ask in prayer, believe that you have received it, and it will be yours" (Mark XI). But it must be noted that we are heard by the Lord when praying in such a way, provided we ask for what he has commanded. …

Commentary on the Catholic Epistles ↗