Here’s the entire verse:
“Even as Sodom and Gomorrah, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire.” (Jude 7)
Notice carefully: it was the physical cities of Sodom and Gomorrah that “suffered the vengeance of eternal fire,” not just the people. In addition, their punishment is “set forth as an example” of what will happen to the unsaved. In 2 Peter, we find an almost identical verse, yet Peter inserts one tiny, significant detail. Look closely:
“And turning the cities of Sodom and Gomorrah into ashes condemned them with an overthrow, making them an example unto all those that after should live ungodly. ” (2 Peter 2:6, italics added).
What was the net result of that “eternal fire” which fell upon Sodom and Gomorrah ? Those cities became ashes. But that’s not all. Describing “the punishment of the sin of Sodom,” Jeremiah said that those evil cities were “overthrown as in a moment” (Lamentations 4:6, italics added). Now put the pieces together. By comparing Jude 7 and 2 Peter 2:6 with Lamentations 4:6, we discover plainly that the “the vengeance of eternal fire” was so incredibly hot that it reduced Sodom and Gomorrah “into ashes” in “a moment” of time. Now think about it. Are Sodom and Gomorrah still destroyed? Yes. But are they burning now? Obviously not. Then what does “eternal fire” mean? By comparing Scripture with Scripture, it means that the fire came from God and that the punishment lasts forever, not the flames. And again, both Jude and Peter called this punishment “an example” of what will happen to all the lost.
Jesus Christ also warned that He will someday declare to lost sinners, “Depart from me, you cursed, into everlasting fire prepared for the devil and his angels” (Matthew 25:41, italics added). Is this fire the same type of fire mentioned in Jude 7, one which destroys completely? We know it is because five verses later our Lord clarified, “And these [the lost] shall go away into everlasting punishment, but the righteous into life eternal” (Matthew 25:46). Thus the lost experience “everlasting punishment,” not punishing, just like the Sodomites."