John Calvin Commentary Jude 1:11

"Woe unto them! For they went in the way of Cain, and ran riotously in the error of Balaam for hire, and perished in the gainsaying of Korah." — Jude 1:11 (ASV)

Woe unto them. It is a wonder that he denounces them so severely, especially since he had just said that an angel was not permitted to bring a railing accusation against Satan. However, his purpose was not to lay down a general rule; he only showed briefly, through the example of Michael, how intolerable their madness was when they insolently reproached what God honored.

It was certainly lawful for Michael to pronounce his final curse against Satan, and we see how vehemently the prophets threatened the ungodly. But when Michael refrained from extreme severity (which was otherwise lawful), what madness was it for them to observe no moderation towards those excelling in glory? But when he pronounced woe on them, he did not so much call down evil on them as remind them of the kind of end that awaited them; and he did this so that they would not carry others with them to perdition.

He says that:

1. They were the imitators of Cain, who, being ungrateful to God and perverting His worship through an ungodly and wicked heart, forfeited his birthright.
2. They were deceived like Balaam by a reward, because they corrupted the doctrine of true religion for the sake of dishonest gain. He adds that they overflowed, a metaphor signifying that their excess was like overflowing water.
3. They imitated the contradiction of Korah, because they disturbed the order and peace of the church.