Although you are fully aware of this, I want to remind you that after Jesus had delivered His people out of the land of Egypt, He destroyed those who did not believe.
KJV
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.
ASV
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.