Charles Spurgeon Commentary Mark 4:38

"And he himself was in the stern, asleep on the cushion: and they awake him, and say unto him, Teacher, carest thou not that we perish?" — Mark 4:38 (ASV)

And he was in the hinder part of the ship, asleep on a pillow:

He was quite at home upon the wild waves—"Rocked in the cradle of the deep"—for winds and waves were but his Father's servants, obeying his commands. He was in the hinder part of the ship, asleep on a pillow; doubtless weary and worn with the labors of the day.

We do not always think enough of the weariness of Christ's human body. There was not only the effort of preaching, but his preaching was so full of high thought, and the expressions he used were so pregnant with meaning, that it must have taken much out of him to preach thus from the heart, with intense agony of spirit, and with his brain actively at work all the while.

Remember that he was truly man as well as the Son of God, and that what he did was of so high an order, not to be reached by any of us, that it must have exhausted him. Therefore, he needed sleep to refresh him; and there he was wisely taking it, and serving God by sleeping soundly, and thus preparing himself for the toil of the following day.