5 And hence also is that which was just now read, “Lord, if it be Thou, bid me come unto You on the water.” For I cannot do this in myself, but in You. He acknowledged what he had of himself, and what of Him, by whose will he believed that he could do that, which no human weakness could do. Therefore, “if it be Thou, bid me;” because when you bid, it will be done. What I cannot do by taking it upon myself, You can do by bidding me. And the Lord said “Come.” And without any doubting, at the word of Him who bade him, at the presence of Him who sustained, at the presence of Him who guided him, without any delay, Peter leaped down into the water, and began to walk. He was able to do what the Lord was doing, not in himself, but in the Lord. “For you were sometimes darkness, but now are you light in the Lord.” What no one can do in Paul, no one in Peter, no one in any other of the Apostles, this can he do in the Lord. Therefore well said Paul by a wholesome despising of himself, and commending of Him; “Was Paul crucified for you, or were ye baptized in the name of Paul?” So then, you are not in me, but together with me; not under me, but under Him.
Source: Sermons on Selected Lessons of the New Testament (New Advent)