John Chrysostom
That is, not only in cutting off the sinner, but also in joining him again.
Do you see how here also the Apostle again places them under necessity of resolving upon this struggle?
When the guilty man sinned, the Apostle showed them what danger threatened them if they did not cut him off.
He said that "a little leaven leavens the whole lump" (1 Cor 5:6), and much else.
So also here he again sets before them the whole danger of disobedience.
"Just as before," he says, as it were, "I had to care not only for him, but also for you, so now I care not so much for him as for you.
I do this lest someone regard you as stubborn, inhuman, and not obedient in all things."
Read more (226 words)
Therefore he says: "For to this end I also wrote, that I might know the proof of you, whether you are obedient in all things."
The former act, removing the guilty man from the community, might have seemed an act of hatred and cruelty.
The latter act, receiving him into love, will especially prove the sincerity of obedience and readiness for deeds of love for mankind.
The mark of good disciples is that they obey their teacher not only in his first demand, but also when he commands the opposite of that demand.
Therefore the Apostle said, "in all things." He wished to show that if the Corinthians disobeyed, they would disgrace not so much him as themselves, earning the reputation of the disobedient.
He does this in order to move them to obedience by this also. Therefore he says, "For to this end I also wrote to you."
Though he did not write for this reason, since his chief aim was the salvation of the sinner, he nevertheless says "for this reason" to dispose them more in favor of the guilty man.
Yet by this he neither harms himself in attaining the chief aim, nor fails to show grace to the Corinthians.
By the words "in all things" he reminds them of their first obedience and sets it before them here, intending to praise them.