Woe unto them! for they have gone in the way of Cain, and ran greedily after the error of Balaam for reward, and perished in the gainsaying of Core. They have gone in the way of Cain - They are haters of their brethren, and they that are such are murderers; and by their false doctrine they corrupt and destroy the souls of the people.
The error of Balaam - For the sake of gain they corrupt the word of God and refine away its meaning, and let it down so as to suit the passions of the profligate. This was literally true of the Nicolaitans, who taught most impure doctrines, and followed the most lascivious practices.
Gainsaying of Core - See the account of the rebellion of Korah, Dathan, and Abiram, and their company, in Numbers 22. It appears that these persons opposed the authority of the apostles of our Lord, as Korah and his associates did that of Moses and Aaron; and St. Jude predicts them a similar punishment. In this verse he accuses them of murder, covetousness, and rebellion against the authority of God.