"And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea. And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband. And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God. And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away." (Revelation 21:1-4)
The teaching of a new heaven and earth is not limited to the book of Revelation. The saints of both the Old and New Testaments were well aware of the fact that this sin-cursed universe is temporary. The Psalmist wrote...
Of old hast thou laid the foundation of the earth: and the heavens are the work of thy hands. They shall perish, but thou shalt endure: yea, all of them shall wax old like a garment; as a vesture shalt thou change them, and they shall be changed (Psalm 102:25-26).
Isaiah's prophecies provide some of the clearest Old Testament teaching on this concept.
For, behold, I create new heavens and a new earth: and the former shall not be remembered, nor come into mind. But be ye glad and rejoice for ever in that which I create: for, behold, I create Jerusalem a rejoicing, and her people a joy ... For as the new heavens and the new earth, which I will make, shall remain before me, saith the LORD, so shall your seed and your name remain (Isaiah 65:17-18, 66:22).
Peter would later echo these prophecies when he penned...
But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up ... Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness (II Peter 3:10, 13).
The unbelieving world is terrified by the fact that the world's resources are running out. They consider the slow deterioration of the worlds and are motivated to find a way to sustain life on a space station or to discover a new world on which man can live. In opposition to this hopeless view point, the Christian looks for the new creation - a world in which there is no sin or sorrow. The sentence there was no more sea is likely referring to the fact that trouble, conflict and uncertainty will not be present in the new creation since the sea is often viewed as symbolic of tribulation and unrest.
The full weight of the believer's hope is not found in the establishment of a millennial, earthly Jerusalem but in a heavenly Jerusalem where the saints of all ages will dwell with Christ. Once having passed from death unto life by belief in Jesus Christ, a man's citizenship changes from that of earth to heaven. Paul spoke of this heavenly city when he wrote...
But Jerusalem which is above is free, which is the mother of us all (Galatians 4:26).
But ye are come unto mount Sion, and unto the city of the living God, the heavenly Jerusalem, and to an innumerable company of angels, to the general assembly and church of the firstborn, which are written in heaven, and to God the Judge of all, and to the spirits of just men made perfect, and to Jesus the mediator of the new covenant, and to the blood of sprinkling, that speaketh better things than that of Abel (Hebrews 12:22-24).