Then the angel showed me the river of the water of life, bright as crystal, flowing from the throne of God and of the Lamb through the middle of the street of the city; also, on either side of the river, the tree of life with its twelve kinds of fruit, yielding its fruit each month. The leaves of the tree were for the healing of the nations. – Revelation 22:1-2 ESV
In the second chapter of Genesis, God plants a garden, Eden, and in the midst of the garden is the tree of life. But in the third chapter, Adam and Eve sin and are cast out of the garden to prevent their eating from the tree of life and living forever. A guard is then placed at the entrance to the garden, and this tree is never mentioned again until Revelation.
As a part of the letter to the church at Ephesus (Rev 2:1-7), Jesus tell them that those who conquer will be given the right to eat from the tree of life in God’s paradise. And now, at the opposite end of the Bible from where the tree of life is lost to us, it is once again available for us to eat from. What was lost when paradise (Eden) was closed, is restored in the Holy City (Rev. 21:2, 10), the new paradise of God (Rev. 1:7).
Blessed are those who wash their robes, so that they may have the right to the tree of life and that they may enter the city by the gates. – Revelation 22:14