Some have speculated that Jesus asked Peter a question for each time he had denied Christ (i.e., three). Peter had earlier boasted that he, even if all of the other disciples stumbled, would never stumble (cf. Matt. 26:33). Jesus had correctly predicted otherwise. He now asks Peter if he still claims to love Him more than the other apostles love Him. Peter has been humbled, however, and is no longer willing to compare the depth of his love with the love of his fellow disciples. He is content to merely affirm that he does love Jesus; he does not claim to possess a commitment superior to the others. When Jesus says, "Feed My lambs," He seems to be instructing Peter to recognize his obligation as a teacher and shepherd toward young, immature disciples. Jesus is not giving Peter a position of supremacy over the other apostles (and Peter never claimed such; cf. I Pet. 5:1).
Jesus asks a similar question in John 21:16, and Peter answers as he did the first time. Jesus replies - "Tend My sheep." Here the emphasis is upon the older, mature disciples. Peter has a responsibility to them also. It is interesting to note that all three times Jesus questions him, He calls him "Simon" and not "Peter." This would have been noticed by him since "Peter" was the special name Jesus had given him which meant "rock" (and implied stability and strength; cf. Mark 3:16).
Jesus asks a third time in John 21:17, but He uses a different word for "love" this time. Jesus' first two questions had used the word agape (indicating strong devotion of the highest order), and Peter used the word phileo in all of his responses (indicating the devotion of brotherly association). This time Jesus' question used the word phileo, and this is likely what grieved the disciple. Peter had not been willing to affirm that he loved Jesus with agape love and now Jesus questions whether Peter even loves Him to the extent of phileo. It's as if Jesus is asking: "Simon, do you really have the warm, personal, and abiding affection for me that you claim? Have you forgotten that you stood far off while I was being reviled and even denied that you knew Me?" Jesus' words cut Peter to the heart!
"Lord, You know all things; You know that I love You" - Peter's humility stands the test of this third question. He does not boldly jump forward to stand on his own assurance; he has changed. He humbly answers in a way that shows he has learned a powerful and lasting lesson. He knows he needs to be more cautious and less boastful. He also knows that Jesus already possesses the answer to His own question.
Three times Peter denied the Lord, and three times Jesus required him to reaffirm his love. The process, though painful, was a healing one for Simon and brought him back to a commitment that would remain with him the remainder of his days and prompt him to become one of the most courageous and faithful disciples the Lord ever had. It is interesting to observe that the circumstances of Peter's original call are very similar to those of his restoration (cf. Luke 5:1-11).
"Most assuredly, I say to you when you were younger, you girded yourself and walked where you wished; but when you are old, you will stretch out your hands, and another will gird you and carry you where you do not wish" (John 21:18). When Peter was a young man, he could prepare himself and go where he pleased. However, eventually, as an older man, he would stretch out his hands and be bound and carried to where he did not want to go. "This He spoke, signifying by what death he would glorify God" (John 21:19). Although it is possible that Peter may not have understood Jesus' words, John makes the meaning plain for his readers. Jesus was speaking about how Peter would die (i.e., via crucifixion). It seems likely, however, that Peter did understand exactly what Jesus was saying since he asked about John in 21:21.
"Follow Me" - Peter had previously forsaken Jesus for fear of death, and now, with the absolute certainty of death by martyrdom, he is bidden to resume His Master's work. He certainly did such faithfully and fearlessly from this point on. He followed the Lord in his teaching, work, and--if the tradition is true--manner of death (it is traditionally believed that Peter lived to an old age and was crucified; he requested to be nailed to the cross with his head downward, not deeming it proper to die in the same way as Jesus did). Not only do Jesus' words prophetically foretell of Peter's end, they also vividly contrast his strong, assertive actions of youth with his final act of submission in old age.