And in the fourth watch of the night - The Jews anciently divided the night into three parts of four hours each, usually called watches. The first of these watches is mentioned in Lamentations 2:19, the middle watch in Judges 7:19, and the morning watch in Exodus 14:24. In the time of our Saviour they divided the night into four watches, the fourth having been introduced by the Romans. These watches consisted of three hours each. The first commenced at six and continued until nine; the second from nine to twelve; the third from twelve to three; and the fourth from three to six. The first was called evening; the second midnight; the third cock-crowing; the fourth morning, Mark 13:35. It is probable that the term watch was given to each of these divisions from the practice of placing sentinels around the camp in time of war, or in cities, to watch or guard the camp or city; and that they were at first relieved three times in the night, but under the Romans four times. It was in the last of these watches, or between three and six in the morning, that Jesus appeared to the disciples, so that he had spent most of the night alone on the mountain in prayer.
Walking on the sea - A manifest and wonderful miracle. It was a boisterous sea. It was in a dark night. The little boat was 4 or 5 miles from the shore, tossed by the billows.

The fourth watch - Anciently the Jews divided the night into three watches, consisting of four hours each. The first watch is mentioned, Lamentations 2:19 : the second, Judges 7:19; and the third, Exodus 14:24; but a fourth watch is not mentioned in any part of the Old Testament. This division the Romans had introduced in Judea, as also the custom of dividing the day into twelve hours: see John 11:9. The first watch began at six o'clock in the evening, and continued till nine; the second began at nine, and continued till twelve; the third began at twelve, and continued till three next morning; and the fourth began at three, and continued till six. It was therefore between the hours of three and six in the morning that Jesus made his appearance to his disciples.
Walking on the sea - Thus suspending the laws of gravitation was a proper manifestation of unlimited power. Jesus did this by his own power; therefore Jesus showed forth his Godhead. In this one miracle we may discover three: -
1. Though at a distance from his disciples, he knew their distress.
2. He found them out on the lake, and probably in the midst of darkness.
3. He walked upon the water.
Job, speaking of those things whereby the omnipotence of God was demonstrated, says particularly, Job 9:8, He walketh upon the waves of the sea: intimating that this was impossible to any thing but Omnipotence.

And in the (c) fourth watch of the night Jesus went unto them, walking on the sea.
(c) By the fourth watch is meant the time nearer to day break: for in ancient times they divided the night into four watches in which they posted watches.

And in the fourth watch of the night,.... This is said, according to the division of the night into four watches, by the Jews; who (o) say, that
"there are four watches in the night, and four watches in the day.''
It is true indeed, that it is disputed among them, whether there were four watches, or only three in the night: some say there were four, others say there were but three (p); not but that these made a division of the night into four parts, the three first of which, they thought were properly the watches of the night, and the fourth was the morning. The first watch began at six o'clock in the evening, and lasted till nine; the second began at nine, and ended at twelve, which was midnight; the third began at twelve, and closed at three; the fourth began at three, and ended at six in the morning. But since some (q) Jewish writers are so positive for the division of the night into three watches only, and a watch is with them called (r) the third part of the night; and it is dubious with some, whether the Jewish division is here referred to; and since it is so clear a point, that the Romans (s) divided their night into four watches, and their writers speak not only of the first, second, and third watches, but also of the fourth watch (t); it is thought by some, that the evangelist speaks after the Roman manner: but however, certain it is, that within this period, probably at the beginning of it, after three o'clock in the morning, Christ came to his disciples, when they had been almost all the night at sea, tossed with waves, and in great danger.
Jesus went unto them; from the mountain where he had been praying, the greatest part of the night, to the sea side, and so upon the waters to them; for it follows,
walking upon the sea; as on dry land: though it was so stormy and boisterous, that the disciples, though in a ship, were in the utmost danger, yet he upon the waves, was in none at all; by which action he showed himself to be the Lord of the sea, and to be truly and properly God; whose character is, that he "treadeth upon the waves of the sea", Job 9:8.
(o) T. Hieros. Beracot, fol. 2. 4. Echa Rabbati, fol. 54. 4. (p) T. Bab. Beracot, fol. 3. 1, 2. (q) Jaschi & Kimchi in Jude vii. 19. & in Psal. cxix. 147. (r) Gloss. in T. Bab. Betacot, fol. 2. 1. (s) Alex. ab Alex. Genial. Dier. 1. 4. c. 20. (t) Liv. Hist. 1. 36, c. 24.

In the fourth watch. The Jews, who used to divide the night into three watches, latterly adopted the Roman division into four watches, as here; so that, at the rate of three hours to each, the fourth watch, reckoning from six P.M., would be three o'clock in the morning.
Jesus went to them. The Lord saw their trouble from his mountain-top, and through the darkness of the night, for his heart was all with them; yet would he not go to their relief till his own time came.

The fourth watch - The Jews (as well as the Romans) usually divided the night into four watches, of three hours each. The first watch began at six, the second at nine, the third at twelve, the fourth at three in the morning. If it be thou - It is the same as, Since it is thou. The particle if frequently bears this meaning, both in ours and in all languages. So it means, John 13:14, John 13:17. St. Peter was in no doubt, or he would not have quitted the ship.