Philippians 3:20-21

Our conversation; more exactly, our citizenship: we are citizens of heaven; our King is there; our hearts and thoughts are there; we obey its laws, and look to it as our everlasting home. As Christians are citizens of heaven, and only pilgrims and sojourners here, they should not be greatly influenced by things of earth, or chiefly occupied with its concerns. Their treasure is, and their hearts should be in heaven; whence they look for Christ perfectly to change them into his own glorious image, and raise them for ever to reign with him in the kingdom of their Father. Shall change; at the resurrection.

The working; the almighty power or energy.

To subdue all things unto himself; consequently death also, the last enemy that should be destroyed. See 1Co 15:26, where the destruction of death is mentioned in immediate connection with the subjection of all things to Christ.

1 Thessalonians 4:13-18

Asleep; asleep in Jesus, who have died in union with Christ by faith, verse 1Th 4:14.

Others; the unenlightened heathen, who have no hope of a resurrection and life of blessedness with Christ in heaven.
Will God bring with him; raise from the dead in glorious, immortal bodies, so that they as well as those that remain alive at Christ's coming, shall appear with him in glory. 1Co 15:51-54. Which are alive; when the Lord shall come to judgment.

Shall not prevent; not go before, or rise to meet the Lord before those do who are dead.
Rise first; before the living shall be changed. But after the dead in Christ are raised, the living shall be changed, and both ascend together to be for ever with the Lord. The prospect of meeting our pious friends at the day of judgment, and with them, perfect in body and soul, ascending with Christ and all his redeemed, to be for ever like him, soothes the anguish of parting with them, and fills the soul with joys unspeakable and full of glory.
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