"The scene described here is concerned with the way Peter no longer looks at Jesus but has earthly elements in view. Naturally, then, by any reckoning of probability, he is bound to sink as soon as he gets out into the water. But he has left out of this the essential point, that he has been called by Jesus, who is the Lord. Together with him, and by his power, in relation to him, he will so to speak be able to walk right over even what is deadly in this world."
--Cardinal Joseph Ratzinger (Benedict XVI), God and the World (Ignatius Press, 2000), p. 240