What is the tree of life in Revelation 22?
In Revelation 22 the tree of life is the tree in the midst of New Jerusalem that bears twelve kinds of fruit, one every month, and whose leaves are for the healing of the nations, echoing the same tree that was originally placed in the Garden of Eden to give man everlasting life.
Revelation 22:1-2 describes John seeing a pure river of water of life flowing from the throne of God and of the Lamb, and in the midst of the street, on either side of that river, stood the tree of life. It bore twelve manner of fruits, yielding its fruit every month, and its leaves were for the healing of the nations. This tree is placed in the New Jerusalem, in the new heaven and new earth where there is no more death, sorrow, crying or pain, and where God himself dwells with His people.
This tree is the same kind of tree first placed in the Garden of Eden. Genesis 2:9 shows that the Lord God made the tree of life to grow in the midst of the garden, alongside the tree of knowledge of good and evil. It was placed there so that man could live forever, and its leaves and fruit were good for healing the body. Genesis 2:16-17 records that man was free to eat of every tree, including the tree of life, except the tree of knowledge of good and evil. When Adam disobeyed and ate of the forbidden tree, Genesis 3:22-23 shows that God sent him out of the garden specifically so he would not also take of the tree of life and live forever in his fallen, corrupted state.
So the tree of life in Revelation 22 is the restoration of what was lost in Eden, now placed in the eternal city rather than a garden that could be lost again. Its fruit continually supplies life, and its leaves bring healing to the nations who dwell on the restored earth. Those who are in Christ, the sons of God who reign with Him, are said to have no need of these healing leaves themselves, because they are already made divine and eternal; the healing of the tree is for the nations that inhabit the new earth.
In this way the tree of life stands at both the beginning and the end of the biblical story: first offered and then withheld because of sin, and finally restored fully and permanently in the new heaven and new earth, where mankind can once again live forever and the whole earth is made a paradise again.
The scriptures
And he shewed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb. In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations.
And out of the ground made the LORD God to grow every tree that is pleasant to the sight, and good for food; the tree of life also in the midst of the garden, and the tree of knowledge of good and evil.
And the LORD God commanded the man, saying, Of every tree of the garden thou mayest freely eat: But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
And the LORD God said, Behold, the man is become as one of us, to know good and evil: and now, lest he put forth his hand, and take also of the tree of life, and eat, and live for ever: Therefore the LORD God sent him forth from the garden of Eden, to till the ground from whence he was taken.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.