The apostle provides the examples of Cain, Balaam, and Korah as illustrative of apostates. All of them were rebellious and anti-God at the core but in different ways.
Cain's sin manifested itself in a sullen, selfish hatred that ended up in murder. Balaam's sin was manifested in the form of covetousness and greed, which he used to induce others to sin. (Recall that Jesus says in Matthew 5:19 that whoever teaches against God's law will be least in the Kingdom. These men may not even be there at all. Balaam certainly taught others to sin.)
Korah's sin manifested itself in speaking against the God-appointed authority and attracting a following to wrest away an office that was not his. He is forever an example of that, reaching above his station, as it were. We do not hear much about rising above one's station in these democratic days, but the church is not a democratic society. The church is God's Family, and He places people in His body as it pleases Him (I Corinthians 12:18). Korah had been placed in Israel in a certain spot, and he tried to go above his station, persuading others to do the same and support him in his coup—and he ended up as a black spot in the wilderness of Sinai along with many of his supporters.
Jude, then, is not only showing sin, but also God's judgment and severe punishments for sin.
Richard T. Ritenbaugh