On a spring morning, on the shore of the Lake of Tiberias ...
In Greek, the word "fileo" means the love of friendship, tender but not all-encompassing; instead, the word "agapao" means love without reserve, total and unconditional. Jesus asks Peter the first time: "Simon... do you love me (agapas-me)" with this total and unconditional love (Jn 21: 15)?
Prior to the experience of betrayal, the Apostle certainly would have said: "I love you (agapo-se) unconditionally". Now that he has known the bitter sadness of infidelity, the drama of his own weakness, he says with humility: "Lord; you know that I love you(filo-se)", that is, "I love you with my poor human love". Christ insists: "Simon, do you love me with this total love that I want?". And Peter repeats the response of his humble human love: "Kyrie, filo-se", "Lord, I love you as I am able to love you". The third time Jesus only says to Simon: "Fileis-me?", "Do you love me?".
Simon understands that his poor love is enough for Jesus, it is the only one of which he is capable, nonetheless he is grieved that the Lord spoke to him in this way. He thus replies: "Lord, you know everything; you know that I love you (filo-se)".
This is to say that Jesus has put himself on the level of Peter, rather than Peter on Jesus' level! It is exactly this divine conformity that gives hope to the Disciple, who experienced the pain of infidelity.
From here is born the trust that makes him able to follow [Christ] to the end: "This he said to show by what death he was to glorify God. And after this he said to him, "Follow me'" (Jn 21: 19).
From that day, Peter "followed" the Master with the precise awareness of his own fragility; but this understanding did not discourage him. Indeed, he knew that he could count on the presence of the Risen One beside him. - Benedict XVI
I've been reading a lot of Pope Benedict the past few days.