Verse 25. "The fourth watch" - Anciently the Jews divided the night into three watches, consisting of four hours each. The first watch is mentioned, Lamenations ii. 19: the second, Judg. vii. 19; and the third, Exod. xiv. 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 xi. 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 ix. 8, He walketh upon the waves of the sea: intimating that this was impossible to any thing but Omnipotence.