And there will no longer be any night; and they will not have need of the light of a lamp nor the light of the sun, because the Lord God will illumine them; and they will reign forever and ever.” Revelation 22:1-5. (Emphasis added).
In regards to “a river of the water of life, clear as crystal“, Rev. Herman Hoeksema in his book Behold he Cometh! An Exposition of the Book of Revelation at page 710 on his commentary of Revelation 22:1-5 states: “The river of the water of life, therefore, is symbolic of a constant flow of life, of the continuous operation of the life-giving Spirit of God in Christ which the glorified saints constantly and by a constant act on their part receive and appropriate. … Or, if you will, the reference is to that stream of the blessings of grace, – the blessings of knowledge of God, righteousness, and holiness, of the favor of God, and of all that is implied in life in the true sense of the word, – a constant stream of blessings which flow to the saints through the Spirit of our Lord Jesus Christ.”
In regards to “the tree of life, bearing twelve kinds of fruit“, Rev. Herman Hoeksema in his book Behold he Cometh! An Exposition of the Book of Revelation starting at page 711 on his commentary of Revelation 22:1-5 compares this heavenly tree of life with the tree of life in the Garden of Eden and states about this heavenly tree of life: “In the first place, it symbolizes the perfected life of heavenly fellowship with God, which means that the saints constantly taste God’s covenant friendship. … And, in the second place, the tree of life represents the perpetuation of the glorious life in the resurrection body. … There is never any want of fruit, and therefore never any want of life and immortality, for the church. …”.
In regards to “and they will reign forever and ever“, Rev. Herman Hoeksema in his book Behold he Cometh! An Exposition of the Book of Revelation at page 714 on his commentary of Revelation 22:1-5 states: “With and in Christ the saints shall participate in the reign over all creatures in the new creation. … All things shall serve them, that they may serve their God in Christ. Forever they shall reign! … There will be no possibility of an end, no possibility of a fall any more. …”
Reformed Doctrine Daily Devotions 