Jude 1:7
as Sodom and Gomorrah, and the cities around them in a similar manner to these, having given themselves over to sexual immorality and gone after strange flesh, are set forth as an example,
suffering the vengeance of eternal fire.
Something to think about, the fire that killed them who lived on earth went out, but the fire that burns them in hell did not. They just continue to experience the fire, the eternal fire for those of Sodom did not end.
And yet it will go the worse for those who today do not hear and repent and believe and receive the testimony of Christians about Christ compared to the people of Sodom.
The proper translation is important. Compare the "Interlinear" for Jude 7 via this site:
Jude 1 Interlinear Bible
The Interlinear there says it is not "suffering the vengeance of eternal fire", as your version says, but the cities are "set forth as an example", "undergoing the penalty of fire aionion".
Similarly, a literal version reads:
7 As Sodom and Gomorrah and the cities about them in like manner to these committing ultra-prostitution, and coming away after other flesh, are lying before us, a specimen, experiencing the justice of fire eonian." (Jude 7, CLNT)
"7 The destruction of Sodom and the surrounding cities is still apparent to all who visit the region. In this way these cities are experiencing the justice of eonian fire. The fire has long ceased but its effects will remain and testify to God's judgment until the close of this eon, after which Sodom shall return to her former estate (Ezek.16:53-56)" (Concordant Commentary of the New Testament, p.376)
Concordant Commentary on the New Testament
"We likewise subscribe to the destruction of Sodom and Gomorrah, who "are set forth for an example, suffering the vengeance of eternal fire" (Jude 7). This occurred many centuries ago. How poor a passage to apply to that which is thousands of years hence!"
"The word "set forth" is, literally, "lying before." The term "example" or specimen, is from the word show. These are readily comprehended if we apply them to the sites of Sodom and Gomorrah today. Their destruction was so complete that their exact location is in dispute. Now the preponderance of opinion places them under the shallow end of the Dead Sea. No one can visit this terrible desolation without fully appreciating the force of these words."
"But we are asked to forget this solemn and forceful scene for an "example" which no one can see, and which is not at all "set forth" or "lying before" us. We are asked to forget the fire (Gen.19:24) which destroyed these cities so that the smoke of the plain went up like the smoke of a furnace. The justice or "vengeance" of this fire is all too evident to this very day. It is a powerful reminder of God's judgment which should deter those who are tempted to follow a similar path. This fire is called "eternal." Just now the plain is covered by water, not fire. It was an eonian fire, as is witnessed by its effect for the eon."
"Speaking of Jerusalem, Ezekiel gives us God's thoughts concerning Sodom. "As I live, saith the Lord God, Sodom thy sister hath not done, she nor her daughters, as thou hast done, thou and thy daughters." And again, "When I shall bring again their captivity, the captivity of Sodom and her daughters...then will I bring again the captivity of thy captives in the midst of them...when thy sisters, Sodom and her daughters, shall return to their former estate, then thou and thy daughters shall return to your former estate" (Ezek.16:48,53,55)."
"2 Peter 2:6 gives a parallel passage, where we read that God condemns the cities of Sodom and Gomorrah, reducing them to cinders by an overthrow, having placed them for an example. This is perfectly plain, unless we try to distinguish between the cities and the people, and make conscious cinders suffer from flames beneath the waters of the Dead Sea."
"If the Sodomites were on public exhibition where all could see them suffering in the flames of a medieval hell, we might consider them as set forth as an example, but as no one has ever seen them, and no one can see them, they are no example at all. The cities, however, are lying before us as a specimen of God's eonian justice. The effects of the fire endure for the eon. When Jerusalem is restored, they will be restored."
A Reply To “Universalism Refuted” Part Seven