John Chrysostom
What then does "an angel of light" mean? It means an angel who has boldness to converse with God and who stands before God. But there are also angels of darkness, ministers of the devil, dark and savage. The devil has deceived many in this way, that is, by assuming the appearance of an angel of light, not by becoming one. In exactly the same way, these men wear the mask of apostles, but not their power, for they cannot possess it. Nothing is so diabolical as doing something only for appearance. Who, then, are "ministers of righteousness"? "It is we," he says, "who preach to you the Gospel that contains righteousness." Either he means this, or he means that those false apostles also arrogate to themselves the glory of righteous men. How then shall we know them?
Read more (69 words)
By their works, as Christ said (Mt 7:20). This compels the Apostle to compare his own merits with their evil works, so that the illegitimate teachers may be exposed by such comparison. Again, when he is about to praise himself, he first exposes them. He does this to show the necessity that makes him touch upon this subject, so that no one can reproach him for speaking about himself.