John Calvin Commentary 1 Thessalonians 4:17

"then we that are alive, that are left, shall together with them be caught up in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord." — 1 Thessalonians 4:17 (ASV)

And so we shall be ever. To those who have been once gathered to Christ, he promises eternal life with him. By these statements, the reveries of Origen and of the Chiliasts are abundantly refuted.

For the life of believers, once they have been gathered into one kingdom, will have no end, any more than Christ’s. Now, to assign to Christ a thousand years, so that he would afterwards cease to reign, would be too horrible to mention. Those, however, who limit the life of believers to a thousand years fall into this absurdity, for they must live with Christ as long as Christ himself will exist.

We must also observe what he says — we shall be — for he means that we entertain a hope of eternal life with true benefit only when we hope that it has been expressly appointed for us.