Ask them how exactly someone's flesh is destroyed yet they're still alive.
Well, now, how else is this concept used by Paul and elsewhere in scripture?
Paul says something similar in 1 Timothy:
"
I have handed over Hymenaeus and Alexander to Satan so that they may be taught not to blaspheme."
In that verse, Paul states a goal: Hymenaeus and Alexander would stop blaspheming." The goal is not to kill them, but to correct their behavior. Apparently Paul's preaching and the congregation's urging is insufficient.
And in the case of the Corinthians, whatever has been done to that point (although it's clear the congregation has been encouraging the sin, if anything) has been insufficient, but Paul's goal is still the man's salvation. In neither case is Paul's goal the man's damnation...but in either case, if he does not repent before his death, damnation would be the result.
But where else does Paul use such a concept? Why, on
himself!
To keep me from exalting myself, there was given me a thorn in the flesh, a messenger of Satan to buffet me—to keep me from exalting myself! -- 2 Corinthians 12.
And even from the Old Testament, the same concept again:
So the LORD said to Satan, 'Behold, he is in your power, only spare his life.' Then Satan went out from the presence of the LORD and smote Job with sore boils from the sole of his foot to the crown of his head. -- Job 2. And the result of this, Job says: "
Now my eye sees you, and I despise myself and repent in dust and ashes." -- Job 4
What is the purpose of using Satan against the flesh? Not to condemn, but to
prevent condemnation by physical humiliation. Satan's nature is apparently such that he can't help but take vicious advantage of being unleashed, even knowing God is using his evil for good.