John tells us that he saw the new heaven and the new earth, because the first heaven and the first earth had passed away (Revelation 21:1). This is covenantal language, which implies, first of all, that all things were fulfilled under the Old Covenant (Matthew 5:18), so it passed away to give place for the New Covenant. Secondly, the Old Covenant was represented in the embroidery on the veil of the Temple, symbolically picturing the heavens and the earth. Therefore, when Jerusalem and the Temple were destroyed in 70 AD, “the first heavens and the first earth” were set on fire and destroyed, thus bringing the Old Covenant to an abrupt end, ushering in the new heavens and the new earth. In other words, the destruction of Jerusalem and the Temple established the New Covenant. This is what John said he foresaw take place.
Moreover, John tells us there was no sea under the new heavens and the new earth! But, how could this be literally true, if the reign of the Messiah extends from sea to sea and from the river to the ends of the earth, meaning from the springs of the river to where it empties into the sea, where the continent or island ends (Psalm 72:8; Zechariah 9:10)? The word of God cannot be made to contradict itself (John 10:35). Therefore, we must read it in such a manner that we seek agreement in all the Scriptures. Therefore, we need to look for a non-literal or a spiritual interpretation for sea in Revelation 21:1.
The prophet tells us that the wicked are like a troubled sea that cannot rest (Isaiah 57:20). The four great empires that affected the Jews came up out of the troubled sea (Daniel 7:1-3). The seven headed beast of the Apocalypse also arose out of the sea (Revelation 13:1). In other words, all these things arose out of the wickedness of men, which is likened to a troubled sea in Isaiah 57:20. Therefore, at the Second Coming of Christ, the heavens and the earth were dissolved with ‘fervent heat’ and were replaced with righteousness (2Peter 3:12-13). In other words, the Old Covenant was powerless to destroy the sea of wickedness, out of which the evil influence of the nations dominated the people of God. Thus, although the Old Covenant condemned evil, it permitted all kinds of evil to influence God’s people. This sea of wickedness won’t be found under the new heavens and the new earth (the New Covenant). Instead, righteousness (no sea) rather than wickedness (the sea) will dwell there (Revelation 21:1). Put another way, under the new heavens and the new earth the people of God will influence the nations (cp. Daniel 2:44), instead of the nations influencing the people of God, as was done under the Old Covenant.
Next, John says he saw New Jerusalem, coming down from God out of heaven, prepared as a bride for her husband (Revelation 21:2). New Jerusalem, or the Bride of Christ, is the Church of the first century AD together with the elect under the Old Covenant. Keep in mind that to ‘come down out of heaven from God’ would be the same as stepping out of the Most Holy Place—where the Lord’s throne is—onto the earth. In the context of Revelation 21:2, this would be the Bride came out of the Most Holy Place and stepped into the Holy Place, the Lord’s footstool (Isaiah 66:1), or where heaven and earth met (Psalm 132:7).
The text says the Bride had been prepared and adorned for her Husband, Christ. In Revelation 19:7 the Bride represents the people of God, while in Revelation 21:2, she represents the city of God (cp. her adornment in verses 18-21). Nevertheless, many people make up a city, so the two are really the same thing. The city’s (the elect’s) adornment is gold, silver and precious stones (Revelation 21:18-21), which simply refers to the labors of the elect in Christ (1Corinthians 3:11-15). Whatever is able to go through the fire (viz. the lake of fire, which is the second death—Revelation 21:8) will be rewarded and count as the Bride’s adornment for her Husband.
 More about this when we get to verse-8.