Genesis 3:24

So He drove out the man; and He placed at the east of the Garden of Eden cherubim, and a flaming sword which turned every way, to keep the way of the tree of life. After his expulsion, man's return into the garden was rendered impossible by the fact that God on the east side, the only accessible entrance, stationed cherubim, armed with the flame of a sword that was two-edged and sharp, glittering in the light as the rays struck its brilliant play. To attempt to pass meant certain death. Man would henceforth know of the existence of Paradise, would even know the location of the tree of life, whose supernatural powers had not been removed by God, but man could not return. This fact was to remind him continually of the time of the final perfection, when sin will be destroyed forever, death will be abolished, and the true tree of life will bear fruit for those that partake of salvation throughout eternity, Revelation 20, 21.