4 Let us question the Lord with such little understanding as we have, and in most humble discourse hold converse with so great a Master. What sayest Thou, O Lord, Thou good Shepherd? For You are the good Shepherd, who art also the good Lamb; at once Pastor and Pasturage, at once Lamb and Lion. What sayest Thou? Let us give ear and aid us, that we may understand. “I,” says He, “am the good Shepherd.” What is Peter? Is he either not a shepherd, or a bad one? Let us see, if he be not a shepherd.
“Do you love Me?” You said to Him Lord, “Do you love Me?” And he answered, “I do love You.” And Thou to him, “Feed My sheep.” Thou, You, Lord, by Your Own questioning, by the strong assurance of Your Own words, made of the lover a shepherd. He is a shepherd then to whom You committed Your sheep to be fed. You Yourself entrusted them, he is a shepherd. Let us now see whether he be not a good one. This we find by the very question, and his answer. You asked, whether he loved You; he answered, “I do love You.”
Thou saw his heart, that he answered truth. Is he not then good, who loves so great a Good? Whence that answer drawn from his inmost heart? Wherefore was this Peter, who had Your eyes in his heart for witnesses, sad because You asked him not once only, but a second and a third time, that by a threefold confession of love, he might efface the threefold sin of denial; wherefore, I say, being sad that he was asked repeatedly by Him who knew what He was asking, and had given what He heard; wherefore being sad, did he return such an answer, “Lord, You know all things, You know that I love You”?
What! In making such a confession, such a profession rather, would he lie? In truth then, he made answer of his love to You, and from his inmost heart he gave utterance to a lover's words. Now You have said, “A good man out of the good treasure of the heart brings forth good things.” So then he is both a shepherd, and a good shepherd; nothing it is true to the power and goodness of the Shepherd of shepherds; but nevertheless even he is both a shepherd, and a good one; and all other such are good shepherds.
Source: Sermons on Selected Lessons of the New Testament (New Advent)