in a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed.
To confirm what he had said of this change, I. He here tells them what had been concealed from or unknown to them till then - that all the saints would not die, but all would be changed. Those that are alive at our Lord's coming will be caught up into the clouds, without dying, Th1 4:11.
Commenting on 1 Corinthians 15:51-57
the last trump--at the sounding of the trumpet on the last day [VATABLUS] (Mat 24:31; Th1 4:16). Or the Spirit by Paul hints that the other trumpets mentioned subsequently in the Apocalypse shall precede, and that this shall be the last of all (compare Isa 27:13; Zac 9:14).
52. In a moment This is still of a general nature; that is, it includes all. For in all the change will be sudden and instantaneous, because Christ’s advent will be sudden. And to convey the idea of a moment, he afterwards makes use of the phrase twinkling (or jerk) of the eye, for in the Greek manuscripts there is a twofold, reading — ῥοπὣ...