Theophylact of Ohrid

"Be not ye therefore like unto them: for your Father knoweth what things ye have need of, before ye ask Him." It is not to inform God of anything that we make our petitions, but instead, that we may detach ourselves from the cares of life and receive benefit by conversing with God.

Commentary on Matthew ↗

Jerome

For your Father knows what you need before you ask him. So you will pray like this. In this place, a certain heresy arises, as well as a perverse doctrine of philosophers, who say: If God knows what we pray for, and before we ask, he knows what we need, then we speak in vain to the one who knows. To these it must be briefly answered, we are not storytellers, but askers. For it is one thing to tell the ignorant, another to ask the one who knows. In that, there is evidence; here, there is obedience. …

Commentary on Matthew ↗

Gregory the Dialogist

And it should be noted what He says to the blind man as he approaches: "What do you want Me to do for you?" Did He who was able to restore light not know what the blind man wanted? But He wishes to be asked for that which He foreknows both that we will ask and that He will grant. For He urges us persistently to prayer, and yet says: "For your heavenly Father knows what you need before you ask Him." Therefore He requires to be asked for this reason: He requires it in order to arouse the heart to prayer.

Forty Gospel Homilies, Homily 2 ↗

Thomas Aquinas

For they think, etc. Be not you therefore like to them, etc., and why: for your Father knoweth, etc.: "Lord, before you is all my desire" (Ps 38:9). Therefore, if he knows, we should not multiply words. But it will be said: God knows what things are necessary for us. Why then do we pray? And Jerome answers that we do not ask with words in order to signify, but in order to petition. And again it could be asked: Why do we utter words? …

Commentary on Matthew ↗