That then they shall see the Son of man coming in the clouds of heaven, with power and great glory.
Note, First, The judgment of the great day will be committed to the Son of man, both in pursuance and in recompence of his great undertaking for us as Mediator, John v. 22, 27.
Secondly, The Son of man will at that day come in the clouds of heaven. Much of the sensible intercourse between heaven and earth is by the clouds; they are betwixt them, as it were, the medium participationis--the medium of participation, drawn by heaven from the earth, distilled by heaven upon the earth. Christ went to heaven in a cloud, and will in like manner come again, Acts i. 9, 11. Behold, he cometh in the clouds, Rev. i. 7. A cloud will be the Judge's chariot (Ps. civ. 3), his robe (Rev. x. 1), his pavilion (Ps. xviii. 11), his throne, Rev. xiv. 14. When the world was destroyed by water, the judgment came in the clouds of heaven, for the windows of heaven were opened; so shall it be when it shall be destroyed by fire. Christ went before Israel in a cloud, which had a bright side and a dark side; so will the cloud have in which Christ will come at the great day, it will bring both comfort and terror.
Thirdly, He will come with power and great glory: his first coming was in weakness and great meanness (2 Cor. xiii. 4); but his second coming will be with power and glory, agreeable both to the dignity of his person and to the purposes of his coming.
Fourthly, He will be seen with bodily eyes in his coming: therefore the Son of man will be the Judge, that he may be seen, that sinners thereby may be the more confounded, who shall see him as Balaam did, but not nigh (Num. xxiv. 17), see him, but not as theirs. It added to the torment of that damned sinner, that he saw Abraham afar off. "Is this he whom we have slighted, and rejected, and rebelled against; whom we have crucified to ourselves afresh; who might have been our Saviour, but is our Judge, and will be our enemy for ever?" The Desire of all nations will then be their dread.
Those that shall be found alive will then be changed. They shall be caught up together with them in the clouds, to meet the Lord in the air, v. 17. At, or immediately before, this rapture into the clouds, those who are alive will undergo a mighty change, which will be equivalent to dying. This change is so mysterious that we cannot comprehend it: we know little or nothing of it, 1 Cor. xv. 51. Only, in the general, this mortal must put on immortality, and these bodies will be made fit to inherit the kingdom of God, which flesh and blood in its present state are not capable of. This change will be in a moment, in the twinkling of an eye (1 Cor. xv. 52), in the very instant, or not long after the raising up of those that sleep in Jesus. And those who are raised, and thus changed, shall meet together in the clouds, and there meet with their Lord, to congratulate him on his coming, to receive the crown of glory he will then bestow upon them, and to be assessors with him in judgment, approving and applauding the sentence he will then pass upon the prince of the power of the air, and all the wicked, who shall be doomed to destruction with the devil and his angels.
(4.) Here is the bliss of the saints at that day: they shall be ever with the Lord, v. 17. It will be some part of their felicity that all the saints shall meet together, and remain together for ever; but the principal happiness of heaven is this, to be with the Lord, to see him, live with him, and enjoy him, for ever. This should comfort the saints upon the death of their friends, that, although death has made a separation, yet their souls and bodies will meet again; we and they shall meet together again: we and they shall meet together again: we and they with all the saints shall meet our Lord, and be with him for ever, no more to be separated wither from him or from one another for ever. And the apostle would have us comfort one another with these words, v. 18. We should endeavour to support one another in times of sorrow, not deaden one another's spirits, nor weaken one another's hands, but should comfort one another; and this may be done by serious consideration and discourse on the many good lessons to be learned from the doctrine of the resurrection of the dead, the second coming of Christ, and the glory of the saints in that day.
Matthew Henry's Commentary on the Bible