If we guard this faith, we shall be free from condemnation and be adorned with virtues of every kind. For the power of faith is so great that it even buoys up men walking upon the sea. Peter was a man like ourselves, composed of flesh and blood, and living on like foods. But when Jesus said: “Come,” believing, he walked upon the waters, having in his faith a support firmer than any natural ground, and upholding the weight of his body by the buoyancy of his faith. Now as long as he believed, he had firm footing upon the water, but when he doubted, then he began to sink; for as his faith gradually gave way, his body also was drawn down along with it. Realizing his predicament, Jesus, who cures our souls’ sicknesses, said: “O thou of little faith, why didst thou doubt?” Then, strengthened by Him who grasped his right hand, as soon as he had recovered his faith, led by the hand of the Master, he walked upon the waters as before. For the Gospel signifies this indirectly in the words: “And when they got into the boat.” For it does not say, swimming to the boat, Peter got into it, but it gives us to understand that, after retracing the distance he had traversed in going to Jesus, he reentered the boat.
St. Cyril of Jerusalem, Catecheses, Catechesis V.7
Locus Communis 