"Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour" (1 Peter 5:8).
Peter did not fall for lack of warning. He fell because he paid no heed to the warnings given. More than once our Lord told him in set terms what would happen. But, so far as Peter was concerned, the warnings fell on absolutely deaf ears. He could not claim that the rock on which his barque struck and well-nigh foundered was a sunken and uncharted rock; he sailed straight on to it, though its bells were clashing out their warnings and telling him of danger. The reason for Peter's neglect of these repeated warnings was, I believe, twofold.
First of all, he had complete confidence in his own courage. He was by nature a strong and forceful personality, and he honestly believed he could stand up to any menacing peril without flinching. And, secondly, he was so entirely and completely devoted to Jesus that the very idea of defection and cowardice seemed wildly and absurdly impossible. Peter really meant what he said when he declared that with Jesus he was ready to go both to prison and to death. For his love for Jesus was, in very truth, the master-passion of Peter's life. That a man thus strong in will and so entirely devoted to Jesus as Peter was should fall so shamefully and disastrously as he did lends peculiar point and emphasis to the apostolic exhortation, "Let him that thinketh he standeth take heed lest he fall."