Augustine of Hippo

Therefore, to conclude our discussion from where we began, let us pray, and presume upon God: let us live as He commands, and where we falter in this life, let us call upon Him, just as the disciples called upon Him saying: "Lord, increase our faith." And Peter presumed, and faltered: yet he was not despised and drowned, but was uplifted and raised up. Indeed, from where did he presume? It was not from his own strength: it was from the Lord. How? "Lord, if it is You, command me to come to You on the water." For the Lord was walking on the water. "If it is You, command me to come to You on the water. For I know that if it is You, You command and it is done." And He said: "Come." He descended at His command, and trembled in his own weakness. Yet when he trembled, he cried out to Him: "Lord," he said, "save me." Then the Lord reached out His hand to him, and said: "O you of little faith, why did you doubt?" He Himself invited, He liberated the one who was faltering and trembling; so that it might be fulfilled, what is said in the Psalm: "If I said, My foot slips; Your mercy, O Lord, supported me."