Charles Spurgeon Commentary Matthew 14:29-30

"And he said, Come. And Peter went down from the boat, and walked upon the waters to come to Jesus. But when he saw the wind, he was afraid; and beginning to sink, he cried out, saying, Lord, save me." — Matthew 14:29-30 (ASV)

And he said, Come. And when Peter was come down out of the ship, he walked on the water, to go to Jesus. But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me.

When he began to be afraid he began to sink. As long as his confidence in his Master lasted he could walk the waves.