When he saw the wind boisterous, he was afraid - It was by faith in the power of Christ he was upheld; when that faith failed, by which the laws of gravitation were suspended, no wonder that those laws returned to their wonted action, and that he began to sink. It was not the violence of the winds, nor the raging of the waves, which endangered his life, but his littleness of faith.

But when he saw the wind boisterous,.... Or "strong", blowing hard against him, and raising up the waves, which beat with great violence upon him,
he was afraid; though Christ was so nigh him, and he had had such an instance of his power in bearing him up, causing him to walk upon the waters thus far; which shows, that his faith was imperfect:
and beginning to sink; through fear, and the violence of the wind and waves, just ready to be immersed, and go down to the bottom of the sea,
he cried; being in a great fright and much danger, and with great importunity and eagerness,
saying, Lord, save me: I am just going, I shall certainly perish else; still having so much faith in Christ, that he was able to save him in the last extremity.

But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me--(Also see on Mark 6:50.)

When he saw the wind boisterous, he was afraid. He stepped into the water, but the roaring winds and rushing billows were too much for his faith.

He was afraid - Though he had been used to the sea, and was a skilful swimmer. But so it frequently is. When grace begins to act, the natural courage and strength are withdrawn.