This life-giving tree had a place in Paradise (Genesis 2:9), access to which had to be denied to fallen humanity lest he eat of this tree and so remain forever in his sinful state (Genesis 3:24). In the first of his seven letters to the churches, Jesus Christ promised that he would grant to the one who conquers [sin]
the privilege to eat of the tree of life, which is in the paradise of God
(Revelation 2:7). In the present passage, access to that tree is granted to those who wash their robes.
The point is that those who treasure the gospel of the Lamb (Revelation 5:6–9), including his atoning work for sin as well as his victory over Satan, may eat of that life-giving tree in God’s presence so as to live forever. This tree of life
was also mentioned in Revelation 22:2 and will receive mention again in Revelation 22:19.
14 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.