Read it again. It makes sense. :-)
After he drove the man out, he placed on the east side of the Garden of Eden cherubim and a flaming sword flashing back and forth to guard the way to the tree of life.
-- Genesis 3:24
Why? Why did God put a guardian angel at the garden?
I think it's because there is no getting back to the Garden the same way we went out. We disobeyed our way into fallenness, but we cannot obey our way into redemption.
But Jesus could. And did.
He is the way back in.
Then the angel showed me the river of the water of life, as clear as crystal, flowing from the throne of God and of the Lamb down the middle of the great street of the city. On each side of the river stood the tree of life, bearing twelve crops of fruit, yielding its fruit every month. And the leaves of the tree are for the healing of the nations. No longer will there be any curse. The throne of God and of the Lamb will be in the city, and his servants will serve him.
-- Revelation 22:1-3