J.C. Ryle comments on John 6:16-21
Let us notice, in the last place, our Lord Jesus Christ’s power over the waves of the sea. He came to His disciples as they were rowing on the stormy lake, “walking on” the waters. He walked on them as easily as we walk on dry land. They bore Him as firmly as the pavement of the Temple, or the hills around Nazareth. That which is contrary to all natural reason was perfectly possible to Christ.
The Lord Jesus, we must remember, is not only the Lord, but the Maker of all creation. “All things were made by him; and without him was not anything made that was made.” (John 1:3.) It was just as easy for Him to walk on the sea as to form the sea at the beginning–just as easy to suspend the common laws of nature, as they are called, as to impose those laws at the first. Learned men talk solemn nonsense sometimes about the eternal fixity of the “laws of nature,” as if they were above God Himself, and could never be suspended. It is well to be reminded sometimes by such miracles as that before us, that these so-called “laws of nature” are neither immutable nor eternal. They had a beginning, and will one day have an end.
Let all true Christians take comfort in the thought that their Savior is Lord of waves and winds, of storms and tempests, and can come to them in the darkest hour, “walking upon the sea.” There are waves of trouble far heavier than any on the Lake of Galilee. There are days of darkness which test the faith of the holiest Christian. But let us never despair if Christ is our Friend. He can come to our aid in an hour when we do not think, and in ways that we did not expect. And when He comes, all will be calm.