5 Though you already know all this, I want to remind you that the Lorda at one time delivered his people out of Egypt, but later destroyed those who did not believe.

Read Jude 1:5 Using Other Translations

I will therefore put you in remembrance, though ye once knew this, how that the Lord, having saved the people out of the land of Egypt, afterward destroyed them that believed not.
Now I want to remind you, although you once fully knew it, that Jesus, who saved a people out of the land of Egypt, afterward destroyed those who did not believe.
So I want to remind you, though you already know these things, that Jesus first rescued the nation of Israel from Egypt, but later he destroyed those who did not remain faithful.