The following is an excerpt from The MacArthur New Testament Commentary on Revelation 21.

Then I saw a new heaven and a new earth; for the first heaven and the first earth passed away, and there is no longer any sea. (21:1)The phrase kai eidon (I saw) is used throughout Revelation to indicate chronological progression (cf. 6:1, 2, 5, 8, 12; 7:2; 8:2, 13; 9:1; 10:1; 13:1, 11; 14:1, 6, 14; 15:1; 16:13; 17:3; 19:11, 17, 19; 20:1, 4, 11). It has introduced each of the climactic events beginning with the return of the Lord Jesus Christ in 19:11. As chapter 21 opens, all the sinners of all the ages, as well as Satan and his demons, have been sentenced to the lake of fire (20:10–15). With all ungodly men and angels banished forever and the present universe destroyed (20:11), God will create a new realm for the redeemed and the holy angels to dwell in forever.

The phrase a new heaven and a new earth derives from two passages in Isaiah. In Isaiah 65:17 God declared, “For behold, I create new heavens and a new earth; and the former things will not be remembered or come to mind.” In Isaiah 66:22 He added, “ ‘For just as the new heavens and the new earth which I make will endure before Me,’ declares the Lord, ‘so your offspring and your name will endure.’ ” What Isaiah predicted is now a reality in John’s vision.

Kainos (new) does not mean new in a chronological sense, but new in a qualitative sense. The new heaven and the new earth will not merely succeed the present universe in chronological sequence; they will be something brand new, fresh, never before seen. God must create a new heaven and a new earth because the first heaven and the first earth passed away. God originally created the earth to be suitable as mankind’s permanent home. The entrance of sin, however, corrupted the earth and the universe, and God will destroy them (cf. 20:11). What lies ahead for the earth is not a nuclear or an ecological holocaust, but a divine judgment.

The Old Testament describes the pollution and destruction of the present universe. Job 15:15 declares that “the heavens are not pure in His sight.” Isaiah 24:5 adds, “The earth is also polluted by its inhabitants, for they transgressed laws, violated statutes, broke the everlasting covenant.” The psalmist writes, “Of old You founded the earth, and the heavens are the work of Your hands. Even they will perish, but You endure; and all of them will wear out like a garment; like clothing You will change them and they will be changed” (Ps. 102:25–26). The Lord Jesus Christ confirmed that Old Testament teaching when He declared, “Heaven and earth will pass away” (Luke 21:33).

The first hint of what the new heaven and new earth will be like comes in John’s observation that there will no longer be any sea. That will be a startling change from the present earth, nearly three- fourths of which is covered by water. The sea is emblematic of the present water-based environment. All life on earth is dependent on water for its survival, and the earth is the only known place in the universe where there is sufficient water to sustain life. But believers’ glorified bodies will not require water, unlike present human bodies, whose blood is 90 percent water, and whose flesh is 65 percent water. Thus, the new heaven and the new earth will be based on a completely different life principle than the present universe. There will be a river in heaven, not of water, but of the “water of life” (22:1, 17). Without a sea, there can be no hydrological cycle, so that every feature of life and climate will be dramatically different.

From a metaphorical perspective, commentators have seen the absence of the sea as symbolic of the absence of evil. Robert L. Thomas summarizes:  Most justifiably see this void as representing an archetypical connotation in the sea (cf. 13:1; 20:13), a principle of disorder, violence, or unrest that marks the old creation (cf. Isa. 57:20; Ps. 107:25–28; Ezek. 28:8).… It is not that the sea is evil in itself, but that its aspect is one of hostility to mankind. For instance, the sea was what stood guard over John in his prison on Patmos and separated him from the churches of Asia.… The sea is the first of seven evils that John says will no longer exist, the other six being death, mourning, weeping, pain (21:4), the curse (22:3), and night (21:25; 22:5). (Revelation 8–22: An Exegetical Commentary [Chicago: Moody, 1995], 440)