The New Jerusalem: Revelation 21:1-21:21

Revelation 21:1-4 "Now I saw a new heaven and a new earth, for the first heaven and first earth had passed away. Also there was no more sea. Then I, John, saw the holy city, New Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband. And I heard a loud voice from heaven saying, "Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people. God Himself will be with them and be their God. And God will wipe away every tear from their eyes, there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away."
After the thousand years have finished God will create a new heaven, a new earth and there will be no more sea. The New Jerusalem is ready and then descends from heaven to the new earth. God will walk with men again. God will abolish all pain and suffering. Many SDA's believe that we will be in heaven for a thousand years, but I'm afraid that honor is reserved for only the 144,000 and the time has already passed. After the second resurrection and judgement all the former things will pass away and will not be remembered. We wont remember the past, so we won't remember all the bad things like death, suffering and above all sin.
Revelation 21:5-8 "Then He who sat on the throne said "Behold, I make all things new." And He said to me "Write, for these words are true and faithful." And He said to me, "It is done! I am the Alpha and the Omega, the beginning and the end. I will give of the fountain of the water of life freely to him who thirsts. He who overcomes shall inherit all things, and I will be His God and he shall be My son. But the cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death.""
The former life and existence on earth will not be remembered everything will be new. Notice how long it takes God to accomplish this new creation and abolish the past, "It is done!" That's pretty fast. A message is given for salvation, saying, that anyone who thirsts can be saved and that those saved will be God's children and He will be their Father on the new earth. A message and warning is also given to the unrighteous if they continue in their ways they will have their part in the second death.
Revelation 21:9-13 “Then one of the seven angels who had the seven bowls filled with the seven last plagues came to me and talked with me, saying, “Come, I will show you the bride, the Lamb’s wife.” And he carried me away in the Spirit to a great and high mountain, and showed me the great city, the holy Jerusalem, descending out of heaven from God, having the glory of God. Her light was like a most precious stone, like a jasper stone, clear as crystal. Also she had a great and high wall with twelve gates, and twelve angels at the gates, and names written on them, which are the names of the twelve tribes of the children of Israel: three gates on the east, three gates on the north, three gates on the south, and three gates on the west.”
Then we are briefly taken back to the point just prior to the thousand year reign and john has a vision where he is taken up to heaven to see the New Jerusalem descending to the new earth. Her light is like a precious stone, pure and clear as crystal. The high wall prevents the unrighteous from entering her. The twelve gates are symbolic and represent the twelve tribes of Israel. 
Revelation 21:14-21 “Now the wall of the city had twelve foundations, and on them were the names of the twelve apostles of the Lamb. And he who talked with me had a gold reed to measure the city, its gates, and its wall. The city is laid out as a square; its length is as great as its breadth. And he measured the city with the reed: twelve thousand furlongs. Its length, breadth, and height are equal. Then he measured its wall: one hundred and forty-four cubits, according to the measure of a man, that is, of an angel. The construction of its wall was of jasper; and the city was pure gold, like clear glass. The foundations of the wall of the city were adorned with all kinds of precious stones: the first foundation was jasper, the second sapphire, the third chalcedony, the fourth emerald, the fifth sardonyx, the sixth sardius, the seventh chrysolite, the eighth beryl, the ninth topaz, the tenth chrysoprase, the eleventh jacinth, and the twelfth amethyst. The twelve gates were twelve pearls: each individual gate was of one pearl. And the street of the city was pure gold, like transparent glass.”
The city was built to house the 144,000 Israelites and the righteous who believed our Lord and His twelve Apostles. The foundations of Christianity and thus the New Jerusalem are built on the twelve Apostles. The city is measured not to proclaim its great length, breadth and height, but to indicate that Judgement is complete and the city is ready to receive its inhabitants. (see Revelation 11:1 in  The Seven Trumpets  for comparison). The majority of the foundations of the wall of the city contain greenish coloured precious stones. The city itself is not decribed, but the streets are made of pure gold which is transparent. The overall impression of the New Jerusalem is that it represents the ultimate treasure chest, the ultimate prize.