A great tempest - A violent storm; or a "wind" so strong as to endanger their lives. This lake was subject to sudden squalls. Dr. Thomson ("The Land and the Book," vol. ii. p. 59) says: "Small as the lake is, and placid, in general, as a molten mirror, I have repeatedly seen it quiver, and leap, and boil like a caldron, when driven by fierce winds from the eastern mountains."
The ship was covered with the waves - The billows dashed against the ship Mark 4:37, so that it was fast filling and in danger of sinking.
He was asleep - On the hinder part of the vessel, on a pillow, Mark 4:38. It was in the night, and Jesus had retired to rest. He was probably weary, and slept calmly and serenely. He apprehended no danger, and showed to his disciples how calmly one can sleep with a pure conscience, and who feels safe in the hands of God.

Arose a great tempest in the sea - Probably excited by Satan, the prince of the power of the air, who, having got the author and all the preachers of the Gospel together in a small vessel, thought by drowning it, to defeat the purposes of God, and thus to prevent the salvation of a ruined world. What a noble opportunity must this have appeared to the enemy of the human race!

And behold, there arose a great tempest,.... "A great concussion", or "shaking" of the sea; the stormy wind moved the sea, and the waves thereof; and both wind and sea shook the ship, and the men that were in it. Luke calls this tempest a "storm wind", Luke 8:23 and Mark says, it was "a great storm of wind", Mark 4:37 and both use the word "loelaps", which signifies a particular kind of wind, which is suddenly whirled about upwards and downwards; or rather, a conflict of many winds: it seems to be a whirlwind, or hurricane. It is said, that this tempest "arose", not by chance, nor by the power of Satan, but by divine providence; for the trial of the faith of Christ's disciples, and that he might have an opportunity of giving proof of his deity on the sea, as he had lately done in several instances on the dry land. Luke says, that this storm of wind "came down"; referring to the motion and course of the winds, which are exhalations from the earth, raised up into the middle region of the air, from whence they are expelled by a superior force to the lower region, and from thence move in an oblique, slanting manner, downwards. The place where this tempest arose, or into which this storm of wind came down, is here said to be
in the sea. Luke calls it a "lake", and it was the lake of Genesareth. But both Matthew and Mark call it the sea, and is what is sometimes called the sea of Tiberias, and the sea of Galilee; see John 6:1 agreeably to the language of the Jewish (i) writers. To all this, the word "behold!" is prefixed; which is sometimes used, when anything extraordinary and preternatural is spoken of: and this storm seems to be more than an ordinary one; at least, it was very sudden and unexpected: when the disciples entered the ship, the air was serene, and the sea still and quiet; but as soon as they had set sail, at once, on a sudden, this storm came down, with great force into the sea, and lifted up its waves;
insomuch that the ship was covered with the waves; it was just sinking to the bottom, so that they were in the utmost extremity: and what added to their distress was,
but he, Christ,
was asleep. Mark mentions the place where he was asleep, "in the hinder part of the ship"; that is in the stern: where he, as Lord and Master, should be, though to the great concern of his disciples, there asleep; and that in a deep sound sleep, as the word which Luke makes use of signifies; and as appears by the loud repeated call of his disciples to awake him: and though this sleep doubtless arose from natural causes, he being greatly fatigued with the business of the day past; yet was so ordered by the providence of God, to come upon him in such a manner at this time, for the trial of the faith of his disciples. Christ's body needing sleep, and refreshment by it, shows that it was a real human body he assumed; subject to the same infirmities as our's; excepting sin; and is no contradiction to the truth of his divinity, as the Jew (k) suggests. He slept as man, though, as God, he is Israel's keeper, who neither slumbers nor sleeps.
(i) T. Bob. Moed. Katon, fol. 18. 2. Bava Kama, fol. 81. 2. Bereshit Rabba, fol. 86. 2. (k) Vet. Nizzachon, p. 210.

There arose a great tempest in the sea. Mark says, "A great storm;" Luke, "There came down a storm of wind;" the word used by Matthew implies a tornado. The Greek word denotes a sudden and violent gust of wind, such as frequently bursts on the lake. All travelers describe the storms as very sudden and violent, caused by the cold air that rushes down from the mountains into the heated depression of the lake.

The ship was covered - So man's extremity is God's opportunity.