Jude now describes what happens to those who don't believe.  He says "Remember", and states three examples.

1.   Jude 1: 5  The Lord saved the people out of Egypt and "…afterward destroyed those that believed not."

2.   Jude 1: 6  "The angels which kept not their first estate, but left their own habitation,…"  (Probably those angels that took sides with Lucifer when he tried to elevate himself over God.)  God says that he has reserved a place in everlasting chains under darkness until the judgement day.  I think that means 'Dead angels walking.'

3.   Jude 1: 7-8   In this verse God describes what happened to Sodom and Gomorrha and will happen to other such cities who give themselves to fornication and "…strange flesh…".  He sets forth an example, damning them to suffering the vengeance of eternal fire.  Likewise, he includes:  1.  Filthy dreamers,  2.  Defilers of the flesh, and  3.  Those who speak evil of 'dignities'.   I don't think I need to spell out what God is saying.  He is warning us that what we 'think' of such things doesn't matter.  What God thinks is what is important.

Jude 1: 9b, 10b, 11a  Jude tells us about a confrontation that the angel Michael had with satan.  "The Lord rebuke you,"  Michael said.  "…they corrupt themselves."  "Woe to them!  for they have gone the way of Cain and ran greedily after of error of Balaam…"   Clear enough.

God calls for purity.  Undefiled purity.  Of the body, and of the soul.   We aren't pure.  But Christ is, and he has taken up residence in our hearts.