6 Therefore, to finish this discourse with that with which we began it, let us pray, and let us rely on God; let us live as He enjoins; and when we totter in this life, let us call upon Him as the disciples called, saying, “Lord, increase our faith.” Peter both put his trust in Him, and tottered; but notwithstanding he was not disregarded and left to sink, but was lifted up and raised. For his trust whence was it? Not from anything of his own; but from what was the Lord's. How? “Lord, if it be Thou, bid me come unto You on the water.” For on the water was the Lord walking. “If it be Thou, bid me come unto You on the water.” For I know that if it be Thou, Thou biddest, and it is done. “And He says, Come.” He went down at His bidding, but in his own weakness he was afraid. Nevertheless when he was afraid, he cried out, “Lord, save me.” Then the Lord took him by the hand, and said, “O you of little faith, wherefore did you doubt?” He first invited him, He delivered him, as he tottered, and stumbled; that it might be fulfilled which was said in the Psalm, “If I said my foot has slipped, Your mercy, O Lord, aided me.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)