Our Lord asks St. Peter three times if he loves Him (cf. John 21:15-17). Each time St. Peter responds that he does. The third time, however, St. Peter is “distressed” and says, “Lord, you know everything; you know that I love you” (John 21:17). Each positive response prompts a commission from our Lord: “Feed my lambs” (John 21:15), “Tend my sheep” (John 21:16), “Feed my sheep” (John 21:17). Our Lord singles out St. Peter, as the question implies, “[D]o you love me more than these?” (John 21:15).
Why three times? Some commentators point out that these three affirmations are to counterbalance the three denials of St. Peter (cf. John 18:17, 25-27). No doubt this is implied. There is yet another interpretation. In the Mid-East, there is a practice by which a question and answer is repeated between two individuals to formalize an agreement. Such a repetition characterizes a binding resolution. It is an immemorial practice.
Whichever explanation is applicable, something very important is happening here and it involves St. Peter. “Amen, amen, I say to you, when you were younger, you used to dress yourself and go where you wanted, but when you grow old, you will stretch out your hands, and someone else will dress you and lead you where you do not want to go” (John 21:18). And, then, the Evangelist remarks: “He said this signifying by what kind of death he would glorify God” (John 21:19). It is only appropriate that the first chosen (cf. Matthew 4:18ff.; Mark 1:16-17; Luke 5:10; John 1:42) and the apostle assigned a unique commission (cf. Matthew 16:17-19) should be the apostle to whom the sheep are entrusted.