After correcting rash judgment and imprudent speech, the Lord now strengthens the soul with confidence in prayer. For many hesitate to ask because they distrust either the goodness of God or their own worthiness. The Lord removes both fears by commanding persistence and promising a response.

The threefold exhortation—ask, seek, knock—does not signify different prayers, but the same desire advancing in intensity. One asks when one begins to pray; one seeks when one persists; one knocks when one perseveres despite delay. Thus the soul is taught not merely to pray, but to remain in prayer until desire itself is purified and enlarged.

The promise that everyone who asks receives is not to be understood of all things without distinction, but of those things that are truly good. For God does not grant what would harm, even when it is earnestly desired. Therefore what is denied is not refused in cruelty, but withheld in mercy.

This is made clear by the comparison with human fathers. Even flawed and sinful parents know not to mock their children’s hunger by offering what is useless or dangerous. If such care exists in those who are imperfect, how much more surely does it exist in the Father who is perfectly good.

Thus the Lord teaches that confidence in prayer rests not on human merit, but on divine fatherhood. God gives as a Father, not as a judge waiting to condemn. And what He gives is always ordered to the true good of the one who asks, even when it does not match what was first sought.

By this teaching the soul is encouraged to persevere without anxiety or presumption—trusting that every sincere prayer is heard, and that every answer, whether given immediately or delayed, is shaped by a love wiser than the one who prays.

Source: St. Augustine, On the Lord’s Sermon on the Mount,  Book II, Chapters 18-19