William Burkitt on 1 Corinthians 15:51

Here the apostle answers a third objection: some might say, What shall become of those who shall be found alive at Christ's coming?

He answers, they shall not die or sleep, but yet shall undergo a change as well as those that rise from the dead, these shall have flesh and blood changed into spiritual bodies, as well as they, and of mortal be made immortal, of corruptible become incorruptible, and all this in a moment of time. Christ's powerful voice will be like a trumpet, calling men together; and the dead shall be raised, and living saints changed into an incorruptible state.