Genesis 3:24 He drove out the man, and at the east of the garden of Eden he placed the cherubim and a flaming sword that turned every way to guard the way to the tree of life.

After Adam and Eve are cast out of the Garden of Eden God places a guardian called a "cherubim" to prevent them from reentering. What is a cherubim? What is the significance of placing the cherubim in the east? There are no mentions of swords before this time, so did God introduce the concept of violent weapons to the world? Why did the sword need to be on fire? Why didn't God just hide the Garden from Adam and Eve?