Jesus' Prayer for Peter and God's Free Gift from "Journeying with the Lord: Reflections for Everyday" by Cardinal Carlos Maria Martini, SJ:

Like a cold shower, the words of Jesus strike Peter: "'Simon, Simon! Satan, you must know, has got his wish to sift you all like wheat; but I have prayed for you Simon, that your faith may not fail, and once you have recovered, you in your turn must strengthen your brothers.' 'Lord,' he answered, 'I would be ready to go to prison with you, and to death.' Jesus replied, 'I tell you, Peter, by the time the cock crows today you will have denied three times that you know me' " (Lk 22:31-34).

How does Peter take these important words: "You must strengthen your brothers"?

Evidently, he assumes that he is capable of assuming the responsibility that the message contains: "Lord, I am ready to go with You to face prison and death." Because we know what happens next, we think of how presumptuous Peter is in making such claims. But the words are so beautiful; words that every Christian should be able to affirmatively say. So, what is bad about them, which will help us to understand how Peter fell? Peter truly expresses what he feels, but it's clear that he didn't hear what Jesus was telling him: "Satan has got his wish to sift you all like wheat; but I have prayed for you, Simon." If Peter had heard this, he would have said: "Lord, thank You for praying for me. I am so weak; I can do so little. Stay near to me." Instead, Peter takes the task on as a privilege which he can handle by his own strength. He misses that the task can only be accomplished through the gift of the Lord. He thus sets himself up for his fall. In fact, the Gospel is precisely the free gift of God. It's the salvation that God freely gives to the sinner. When we receive it with a grateful spirit, with humility and just recognition of its source, we are in our proper place. We can thus begin to appropriate it, digest it and control any situation. Peter thinks he is not afraid, yet his pride comes from his fear of the cross. He is sincere, but his fault lies in his desire to be first. In a theological sense, we could say that he wants to be the Lord's savior.