"And the angels..." - even the angels fear God and are subject to God and experience his judgment if they sin.

"...who did not stay within their own position of authority..." - again, heresy comes when we deny our only Master (Jude 1:4)

"...but left their proper dwelling..." - God has given us a "dwelling place" among the authority structure of the world. We are subject to people, our bosses, parents, government, etc. We are also under God's authority. However, we can leave that place, but it always leads to consequences. We lose our jobs, our families, our freedom, and ultimately eternal happiness.

"he has kept in eternal chains under gloomy darkness until the judgment of the great day" - If this is the fate of angels, what are we doing thinking we might avoid such judgment for our sin? Only in Christ can we have any hope to avoid such terrible eternity.

"just as Sodom and Gomorrah and the surrounding cities, which likewise indulged in sexual immorality" - Here we get another clue as to the sins of Jude's readers: sexual immorality. So, sexual immorality is the heretical indulgence of their flesh.

"and pursued unnatural desire" - The topic of homosexuality is huge these days, with several states now legalizing homosexual marriage. This short phrase, "pursued unnatural desire," is very instructive in helping me understand the nature of homosexuality and homosexual sin. 1) It is a very real desire, and probably not a completely unusual one. 2) It is an unnatural desire. What does that mean, exactly? I think it refers to the idea that we have a "proper dwelling" under the authority of God, and that we are subject to the way he made us and the laws he's put into our world for our good. I don't think "unnatural" means that it is against human nature. In fact, it is human nature to sin in many ways, and to even invent sin for our own temporary joy. 3) Homosexual sin arrives, not necessarily in the desire, but in the pursuit. It is one thing to have a desire and to leave it behind for he sake of Christ. It is another altogether to have that desire and then pursue it for selfish pleasure, using freedom in Christ as the justification for sin. Here is where we decide who is our God and whose authority we will live under, and here is where we move from sin to heresy.

"serve as an example by undergoing a punishment of eternal fire." - We must pay attention to the example of the angels and Sodom and Gomorrah. We will not escape judgment.

Jude 1:6-7