ISB ~ Revelation 21 v1

new heaven . . .new earth:Not entirely new, but entirely renewed (21:5). John sees all creation transformed and made radiant with the glory of God. It is no longer a world subject to death and decay and suffering the damaging effects of human sin (Gen 3:17-18; Rom 8:20-22). The process of cosmic regeneration has begun in the New Covenant as believers are made part of the new creation in Christ (2 Cor 5:17), but John is presented with heaven and earth once this process is complete (CCC 1042-48).

• The imagery comes from Isaiah, who prophesies a new beginning for Israel and the world in terms of a new creation (Is 65:17). He envisions this in connection with the universal worship of the Lord by all flesh (Is 66:22-23).

the sea was no more:The abode of death and evil will be drained away (13:1; 20:13; 21:4). In apocalyptic and poetic texts, the sea often represents chaos and the habitation of all things dreadful and demonic (Job 7:12; Ps 74:13; Is 27:1; Dan 7:3).