Theophylact of Ohrid
Catena Aurea · Lukasevangelium 22
And the Lord said, Simon, Simon, behold, Satan hath desired to have you, that he may sift you as wheat: But I have prayed for thee, that thy faith fail not: and when thou art converted, strengthen thy brethren. And he said unto him, Lord, I am ready to go with thee, both into prison, and to death. And he said, I tell thee, Peter, the cock shall not crow this day, before that thou shalt thrice deny that thou knowest me.
From hence we draw a great doctrine, that human resolve is not sufficient without the Divine support. For Peter with all his zeal, nevertheless when forsaken of God was overthrown by the enemy.