Scripture: Genesis 3:22-24
And the Lord God said, “The man has now become like one of us, knowing good and evil. He must not be allowed to reach out his hand and take also from the tree of life and eat, and live forever.”23 So the Lord God banished him from the Garden of Eden to work the ground from which he had been taken. 24 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.
God put up a barrier between humanity and the Tree of Life. Why did He do this? He says that if humans were to reach out their hand and eat from it, they would live forever. But doesn't God want us to live forever? Doesn't He want us to have eternal life?
As God makes clear in the coming of Christ, He does want us to have eternal life, but it can't come by our own doing. In our sinful state, we can't reach out our hand and take from the Tree of Life. Eternal life is something that God has to give us and lead us toward.
He leads us to the Tree of Life and eternity by guiding us into His wisdom (Proverbs 3) and through belief in His Son (Revelation 22).
We will eat from the Tree of Life, but it will not be because of our strength or actions. We can't reach out our hand and take it for ourselves. It will come only as a gift from God and from what He has done for us by teaching us and sending Christ to take away the barriers between our sinfulness and God's holiness.