What does Revelation 21:1 mean?

John saw a vision of a new heaven and a new earth replacing the millennial heaven and earth. "The heavens" as referred to here, does not include the heaven where God dwells. The word translated as "heaven" most likely refers to earth's atmosphere and/or space.

John writes that the first heaven and the first earth pass away, a statement that some Bible scholars interpret as complete annihilation. Others interpret it to mean a renovation. Those who believe earth and heaven will cease to exist point to Peter's statement that "the heavens and earth that now exist are stored up for fire" (2 Peter 3:7). Those who believe the heavens and the earth will undergo a renovation recall that God destroyed the earth with a flood in the time of Noah, but a new kind of earth emerged when the flood subsided.

The word "new" in Revelation 21:1 is kainon, meaning "new in quality or fresh." Another word for "new" is neos, meaning "new in time." According to this verse, there will not be a sea on the new earth. The absence of a sea assures us this verse does not refer to the millennial earth, because during the millennium large bodies of water will exist (Isaiah 11:9; Ezekiel 47:8–10, 15, 17–20; 48:28; Zechariah 9:10; 14:8). It must describe the eternal earth.