14 “And he brought him to Jesus; and when Jesus beheld him, He said, You are Simon the son of Joannes: you shall be called Cephas, which is, by interpretation, Peter.” It is not a great thing that the Lord said whose son Peter was. What is great to the Lord? He knew all the names of His own saints, whom He predestinated before the foundation of the world; and do you wonder that He said to one man, You are the son of this man, and you shall be called this or that? Is it a great matter that He changed his name, and converted it from Simon to Peter?
Peter is from petra, a rock, but the petra [rock]; is the Church; in the name of Peter, then, was the Church figured. And who is safe, unless he who builds upon the rock? And what says the Lord Himself? “He that hears these my words, and does them, I will liken him unto a wise man building his house upon a rock” (he does not yield to temptation). “The rain descended, the floods came, the winds blew, and beat upon that house; and it fell not: for it was founded upon a rock.
But he that hears my words, and does them not” (now let each one of us fear and beware), “I will liken him to a foolish man, who built his house upon the sand: the rain descended, the floods came, the winds blew, and beat upon that house; and it fell: and great was the fall of it.” What profit is it to enter the Church for him who builds upon the sand? For, by hearing and not doing, he builds indeed, but on the sand. For if he hears nothing, he builds nothing; but if he hears, he builds.
But we ask, Where? For if he hears and does, he builds upon the rock; if he hears and does not, he builds upon the sand. There are two kinds of builders, those building upon the rock, and those building upon the sand. What, then, are those who do not hear? Are they safe? Does He say that they are safe because they do not build? They are naked beneath the rains, before the winds, before the floods; when these come, they carry away those persons before they overthrow the houses.
It is then the only security, both to build, and to build upon the rock. If you will hear and do not, you build, but you build a ruin: and when temptation comes it overthrows the house, and carries away you with the ruin. But if you do not hear, you are naked; you yourself art dragged away by those temptations. Hear, then, and do; it is the only remedy. How many, perchance, on this day, by hearing and not doing, are hurried away on the stream of this festival! For, through hearing and not doing, the flood comes, this annual festival; the torrent is filled, it will pass away and become dry, but woe to him whom it shall carry away!
Know this, then, beloved, that unless a man hears and does, he builds not upon the rock, and he does not belong to that great name which the Lord so commended. For He has called your attention. For if Simon had been called Peter before, you would not have so clearly seen the mystery of the rock, and you would have thought that he was called so by chance, not by the providence of God; therefore God willed that he should be called first something else, that by the very change of name the reality of the sacrament might be commended to our notice.
Source: Tractates on the Gospel of John (New Advent)