Jamieson, Fausset and Brown on Jude 1:11

11. Woe--See on 2Pe 2:14, "cursed children."

Cain--the murderer: the root of whose sin was hatred and envy of the godly, as it is the sin of these seducers.

ran greedily--literally, "have been poured forth" like a torrent that has burst its banks. Reckless of what it costs, the loss of God's favor and heaven, on they rush after gain like Balaam.

perished in the gainsaying of Core--(compare Note, see on Jude 12). When we read of Korah perishing by gainsaying, we read virtually also of these perishing in like manner through the same: for the same seed bears the same harvest.