John Calvin Commentary Jude 1:5

"Now I desire to put you in remembrance, though ye know all things once for all, that the Lord, having saved a people out of the land of Egypt, afterward destroyed them that believed not." — Jude 1:5 (ASV)

I will therefore put you in remembrance, or, remind you. He either modestly excuses himself, for fear that he might seem to be teaching the ignorant, as it were, things unknown to them; or, indeed, he openly declares in an emphatic manner (which I prefer), that he presented nothing new or previously unheard of, so that what he was going to say might gain more credit and authority. I only recall, he says, to your mind what you have already learned.

Just as he credits them with knowledge, he also says that they needed warnings, so they would not think the effort he undertook for them was unnecessary. For the purpose of God’s word is not only to teach what we could not have otherwise known, but also to stir us to serious meditation on those things we already understand, and not to allow us to become lethargic in a cold knowledge.

Now, the meaning is that after being called by God, we should not carelessly glory in his grace but, on the contrary, walk watchfully in his fear. For if anyone thus trifles with God, contempt for his grace will not go unpunished.

And this he proves by three examples. He first refers to the vengeance God executed on those unbelievers, whom he had chosen as his people and delivered by his power. A similar reference is made by Paul in 1 Corinthians 10. The significance of what he says is that those whom God had honored with the greatest blessings, whom he had exalted to the same degree of honor as we enjoy today, he afterwards severely punished. Therefore, their pride in God’s grace was in vain, as they did not live in a manner suitable to their calling.

The word people is used honorifically for the holy and chosen nation, as if he had said that it benefited them nothing that by a special favor they had been brought into covenant. By calling them unbelieving, he indicates the fountain of all evils; for all their sins, mentioned by Moses, were due to this: they refused to be ruled by God’s word. For where there is the submission of faith, obedience towards God necessarily appears in all the duties of life.