Jude 1:7

7.Even as Sodom and Gomorrha. This example is more general, for he testifies that God, excepting none of mankind, punishes without any difference all the ungodly. And Jude also mentions in what follows, that the fire through which the five cities perished was a type of the eternal fire. Then God at that time exhibited a remarkable example, in order to keep men in fear till the end of the world. Hence it is that it is so often mentioned in Scripture; nay, whenever the prophets wished to designate some memorable and dreadful judgment of God, they painted it under the figure of sulfurous fire, and alluded to the destruction of Sodom and Gomorrha. It is not, therefore, without reason that Jude strikes all ages with terror, by exhibiting the same view.

When he says, the cities about them in like manner, giving themselves over to fornication, I do not apply these words to the Israelites and the angels, but to Sodom and Gomorrha. It is no objection that the pronoun τούτοις is masculine, for Jude refers to the inhabitants and not to the places. To go after strange flesh, is the same as to be given up to monstrous lusts; for we know that the Sodomites, not content with the common manner of committing fornication, polluted themselves in a way the most filthy and detestable. We ought to observe, that he devotes them to eternal fire; for we hence learn, that the dreadful spectacle which Moses describes, was only an image of a much heavier punishment.