What is the meaning of Matthew 14:28-30?

28 And Peter answered him and said, Lord, if it be thou, bid me come unto thee on the water. 29 And he said, Come. And when Peter was come down out of the ship, he walked on the water, to go to Jesus. 30 But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me. (Matthew 14:28-30 KJV)

William Burkitt’s Commentary

Observe here, 1. The mixture of Peter’s faith and distrust: it was faith that said, Master; it was distrust that said, If it be thou: It was faith that said, Bid me come to thee: it was faith that enables him to step down on the watery pavement: it was faith that said, Lord save me: but it was distrust that made him sink.

O the imperfect composition of faith and fear in the best of saints here on earth! Sincerity of grace is found with the saints here on earth; perfection of grace with the saints in heaven. Here the saints look forth, fair as the moon, which has some spots in her greatest beauties; hereafter they shall be clear as the sun, whose face is all bright and glorious.

Observe, 2. That whilst Peter believes, the sea is as firm as brass under him; when he begins to fear, then he begins to sink. Two hands upheld Peter; the hand of Christ’s power, and the hand of his own faith. The hand of Christ’s power laid hold on Peter, and the hand of Peter’s faith laid hold on the power of Christ. If we let go our hold on Christ, we sink: if he lets go his hold on us, we drown. Now Peter answered his name Cephas, and he sunk like a stone.