The judgement of Sodom and Gommorah is given as a third example of the consequence of the sin of apostasy. Jude's epistle points out that the perverse sin of Sodom and Gommorah is in like manner to the sin of the apostates: fornication and defilement of the flesh. The men that Jude wrote of who crept in unbeknownst to the assembly were turning the grace of God into lasciviousness by committing spiritual fornication.
If marriage is God's beautiful picture of Christ's love for His bride, the Church, then any perversion of marriage must be a manifestation of self-love. For the husband is the head of the wife, even as Christ is the head of the Church; and He is the savior of the body. This verse in Ephesians presents God's view of what marriage is to look like. From Genesis 4 onward the institution has been twisted to fallen man's liking. Where Christ has one betrothed wife who He is the head of, Lamech had two wives subject to him. The patriarch Abraham under the suggestion of his wife Sarai, took their handmaid Hagar, as a concubine, and putting a strain on his relationship to Sarai. If polygamy, adultery, etc. is a departure of God's ideal plan for displaying His Son's relationship to the Church, then homosexuality goes one step further.
The eighth verse gives a summary of how these false teachers behave according to each OT example. It is important to note that it seems to go in reverse order, starting with the example of Sodom and Gomorrah, and finishing with the mixed multide who believed not that were destroyed by the Lord. The people at Sodom and Gomorrah defiled the flesh, through immoral activity. The angels who left their habitation despised the dominion, the Lordship of Christ. They despised the fact that Christ is Lord. The mixed multitude who did not believe the honest report of Caleb and Joshua, who caused all the congregation to murmur against Moses- spoke evil of dignitaries. The false teachers that Jude is warning about do each of these things and much more according to the Jude's epistle.
These three examples of departure from belief and the consequence thereof, get progressively more graphic and intense. In the fifth verse, it is simply stated that the Lord destroyed those who believed not the witness of the spies' report that the land of Canaan was able to be conquered. Not much is said of their attitude or their punishment, other than they who believed not were destroyed. In the sixth verse, however more details are given. It is said that the angels who did not hold fast to their beginning but left their heavenly home, are now kept in everlasting chains under darkness awaiting final judgement. The seventh verse says more than just Sodom and Gomorrah not believing; they gave themselves over to fornication and went after strange flesh. Their punishment is more than just everlasting chains unto the day of judgement; they suffer the vengence of eternal fire.