In Genesis 2:9, we are told that in the midst of the Garden of Eden, God placed the Tree of Life as well as the Tree of the Knowledge of Good and Evil. Adam was permitted to eat of every tree in the garden except for the Tree of the Knowledge of Good and Evil. God warned that if Adam ate of its fruit, he would surely begin to die. (See this article for an explanation of why that is the best understanding).
In Genesis 3, the Bible describes the fall of mankind and how sin, death, and suffering entered the world when Adam disobeyed God’s commandment and ate from the Tree of Knowledge of Good and Evil.
Towards the end of Genesis 3, we read:
Then the Lord God said, “Behold, the man has become like one of us in knowing good and evil. Now, lest he reach out his hand and take also of the tree of life and eat, and live forever—” therefore the Lord God sent him out from the garden of Eden to work the ground from which he was taken. 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. (Genesis 3:22–24)
This raises an interesting question. Why would God prevent Adam from eating from the Tree of Life after he had sinned? The Bible tells us that the last enemy to be destroyed is death (1 Corinthians 15:26). But if death is an enemy, wouldn’t it have been a good thing for Adam to live forever by eating from the Tree of Life?