IV. Having left these instructions with them, he leaves them (v. 9): When he had spoken these things, and had said all that he had to say, he blessed them (so we were told, Luke 24 50); and while they beheld him, and had their eye fixed upon him, receiving his blessing, he was gradually taken up, and a cloud received him out of their sight. We have here Christ's ascending on high; not fetched away, as Elijah was, with a chariot of fire and horses of fire, but rising to heaven, as he rose from the grave, purely by his own power, his body being now, as the bodies of the saints will be at the resurrection, a spiritual body, and raised in power and incorruption. Observe, 1. He began his ascension in the sight of his disciples, even while they beheld. They did not see him come up out of the grave, because they might see him after he had risen, which would be satisfaction enough; but they saw him go up towards heaven, and had actually their eye upon him with so much care and earnestness of mind that they could not be deceived. It is probable that he did not fly swiftly up, but moved upwards gently, for the further satisfaction of his disciples. 2. He vanished out of their sight, in a cloud, either a thick cloud, for God said that he would dwell in the thick darkness; or a bright cloud, to signify the splendour of his glorious body. It was a bright cloud that overshadowed him in his transfiguration, and most probably this was so, Matt 17 5. This cloud received him, it is probable, when he had gone about as far from the earth as the clouds generally are; yet it was not such a spreading cloud as we commonly see, but such as just served to enclose him. Now he made the clouds his chariot, Ps 104 3. God had often come down in a cloud; now he went up in one. Dr. Hammond thinks that the clouds receiving him here were the angels receiving him; for the appearance of angels is ordinarily described by a cloud, comparing Exod 25 22 with Lev 16 2. By the clouds there is a sort of communication kept up between the upper and lower world; in them the vapours are sent up from the earth, and the dews sent down from heaven. Fitly therefore does he ascend in a cloud who is the Mediator between God and man, by whom God's mercies come down upon us and our prayers come up to him. This was the last that was seen of him. The eyes of a great many witnesses followed him into the cloud; and, if we would know what became of him then, we may find (Dan 7 13), That one like the Son of man came with the clouds of heaven, and came to the Ancient of days, and they brought him in the clouds as he came near before him.

Matthew Henry Commentary on the Whole Bible (Concise) (Matthew Henry)

Verses 6-11 They were earnest in asking about that which their Master never had directed or encouraged them to seek. Our Lord knew that his ascension and the teaching of the Holy Spirit would soon end these expectations, and therefore only gave them a rebuke; but it is a caution to his church in all ages, to take heed of a desire of forbidden knowledge. He had given his disciples instructions for the discharge of their duty, both before his death and since his resurrection, and this knowledge is enough for a Christian. It is enough that He has engaged to give believers strength equal to their trials and services; that under the influence of the Holy Spirit they may, in one way or other, be witnesses for Christ on earth, while in heaven he manages their concerns with perfect wisdom, truth, and love. When we stand gazing and trifling, the thoughts of our Master's second coming should quicken and awaken us: when we stand gazing and trembling, they should comfort and encourage us. May our expectation of it be stedfast and joyful, giving diligence to be found of him blameless.