What is New Jerusalem?
New Jerusalem is the holy city that comes down from God out of heaven, the eternal dwelling place of God with His people and the true home and citizenship of those who are in Christ.
New Jerusalem is described as the holy city coming down from God out of heaven, prepared as a bride adorned for her husband. It appears after the first heaven and the first earth pass away, when there is no more sea to separate the nations. A great voice from heaven declares that the tabernacle of God is now with men, that He will dwell among them, and that He will be their God. In this city there will be no more death, sorrow, crying, or pain, for the former things will have passed away.
Inside this city flows a pure river of the water of life, clear as crystal, coming from the throne of God and the Lamb. On either side of the river stands the tree of life, bearing twelve kinds of fruit every month, with leaves for the healing of the nations. This is the final, eternal creation, the paradise restored and made even better than before, where mankind is united and speaks one pure language to call upon the name of the Lord together.
New Jerusalem is also identified as the heavenly city and the place of our present citizenship even now. It is called the city of the living God, the heavenly Jerusalem, joined to an innumerable company of angels and to the spirits of just men made perfect. It is the city of government that will rule the world and the treasure city where the riches of God’s glory are kept, riches given so that believers may be strengthened in the inner man, rooted and grounded in love, and filled with all the fullness of God.
Those who belong to Christ are the citizens of New Jerusalem. They are called sons of God and part of the Royal family, divine and no longer in need of healing leaves as the nations will be. They are the judges of the world and of the angelic host, not judged themselves because they were already judged in this life by walking in the spirit. They are with Jesus on His throne, eternal, and are the mystery that was hidden in the Father, now revealed as citizens of this holy and everlasting city.
The scriptures
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.
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 he shewed me a pure river of water of life, clear as crystal, proceeding out of the throne of God and of the Lamb. In the midst of the street of it, and on either side of the river, was there the tree of life, which bare twelve manner of fruits, and yielded her fruit every month: and the leaves of the tree were for the healing of the nations.
For then will I turn to the people a pure language, that they may all call upon the name of the LORD, to serve him with one consent.
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,
That he would grant you, according to the riches of his glory, to be strengthened with might by his Spirit in the inner man; That Christ may dwell in your hearts by faith; that ye, being rooted and grounded in love, May be able to comprehend with all saints what is the breadth, and length, and depth, and height; And to know the love of Christ, which passeth knowledge, that ye might be filled with all the fulness of God.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.