John Chrysostom

When then having been asked once and again, he called Him to witness who knoweth the secrets of the heart, and then was asked even a third time, he was troubled, fearing a repetition of what had happened before, (for then, having been strong in assertion, he was afterwards convicted,) and therefore he again betaketh himself to Him. For the saying, "Thou knowest all things," meaneth, "things present, and things to come." Seest thou how he had become better and more sober, being no more self-willed, or contradicting? …

Homily on the Gospel of John 88 ↗

Jerome

If the faith of the apostle Peter is shaken by his Lord's passion, it is so that with bitter weeping he may hear the soothing words "Feed my sheep."

Letter 38.1 ↗

Bede

Peter also restrained himself in this inquiry of our Lord's by answering cautiously, for he remembered earlier on, when Christ's passion was drawing near, he had attributed greater constancy to himself than he possessed.

Homilies on the Gospels 2.22 ↗

Thomas Aquinas

Now we have the second examination. In order to avoid a lot of repetition, note that Christ says three times, Feed my lambs, because Peter ought to feed them three ways. First, they are to be fed by being taught: "And I will give you shepherds after my own heart, who will feed you with knowledge and understanding" (Jer 3:15). …

Commentary on John ↗