Revelation 21:8-14
(Rev 21:8 KJV)
But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.

This verse starts out with the word “but” which means there is a contrast between the previous verse which speaks of the true believer and this verse which speaks of the unbeliever. First of all, we must disregard the idea that this verse is speaking of Christians. There is nothing written in Scripture that teaches that a Christian could possibly lose their salvation. The Bible is very clear that when a person becomes saved, they are saved for all eternity. This verse is speaking of the unbelievers because it speaks of them having their part in the lake of fire which is the second death. The second death has no effect upon the true believers as we saw in Revelation 20:5-6. Those who believe that a person can lose their salvation do not have an understanding of the sacrifice of Christ and what it accomplished in the life of the true believer.

(Rev 21:9 KJV)
And there came unto me one of the seven angels which had the seven vials full of the seven last plagues, and talked with me, saying, Come hither, I will show thee the bride, the Lamb's wife.

Now one of the seven angels which had the vials of the last seven plagues now comes to John with a more pleasant task. He now tells John to come to where he is and he is going to show him the bride of Christ which is the Lamb’s wife. This would be the entire body of believers.

(Rev 21:10 KJV)
And he carried me away in the spirit to a great and high mountain, and showed me that great city, the holy Jerusalem, descending out of heaven from God,

The angel takes John away in the spirit to a great and high mountain. This mountain is not a literal mountain but it just shows that John will have an lofty view of the descent of the great city as it descended out of heaven. It was necessary for John to have the best view possible because he must write what he is seeing in this vision. In Scripture, especially in the Old Testament we are introduced to many cities and the inhabitants of those cities are normally identified with those cities and the traits. For example, Ephesus was identified with Diana worship. Rome was identified with Emperor worship. Corinth was identified with disreputable lifestyles. Anyone coming from these three cities would automatically be labeled as being identified with what made the city famous, whether it would be idolatry or a sin-filled lifestyle. Here in Revelation we are going to receive a city type view of the body of believers as we received a temple view of the body of believers in Ezekiel 40-48 which was representative of Christ building the temple of the body of believers.  The true believers are identified with the New Jerusalem.

(Rev 21:11 KJV)
Having the glory of God: and her light was like unto a stone most precious, even like a jasper stone, clear as crystal;

The glory of God in this verse represents his presence as we have seen that He is now among the believers.
(Ezek 43:5 KJV) So the spirit took me up, and brought me into the inner court; and, behold, the glory of the LORD filled the house. Ezekiel had the same type of vision that John did when he was seeing the temple of God which was the future body of believers in their perfection. In Revelation 4:3, we saw that the Jasper stone was as clear as crystal even though the normal characteristic of a Jasper stone is that it is opaque. Here we are told that the light was like the Jasper stone which represents the absolute purity of God because it is clear as crystal. No longer will there be anything hidden because there are no more mysteries and that is why the Jasper stone is seen as being clear as crystal instead of opaque.

(Rev 21:12 KJV)
And had a wall great and high, and had twelve gates, and at the gates twelve angels, and names written thereon, which are the names of the twelve tribes of the children of Israel:

(Ezek 48:30-35 KJV) And these are the goings out of the city on the north side, four thousand and five hundred measures. {31} And the gates of the city shall be after the names of the tribes of Israel: three gates northward; one gate of Reuben, one gate of Judah, one gate of Levi. {32} And at the east side four thousand and five hundred: and three gates; and one gate of Joseph, one gate of Benjamin, one gate of Dan. {33} And at the south side four thousand and five hundred measures: and three gates; one gate of Simeon, one gate of Issachar, one gate of Zebulun. {34} At the west side four thousand and five hundred, with their three gates; one gate of Gad, one gate of Asher, one gate of Naphtali. {35} It was round about eighteen thousand measures: and the name of the city from that day shall be, The LORD is there.

There is great similarity between the city which Ezekiel saw in his vision and the city which John saw. Each one of the twelve gates has the name of a tribe of Israel. In Revelation 7, where God stated that there were 12,000 from every tribe in Israel, we noticed that Dan was missing but in Ezekiel, the tribe of Dan is included. Once again we must remember that there were more than 12 tribes so what we have in view here represented by the number 12, is the fullness of what is in view. God is using the number 12 to teach us that the New Jerusalem will have the fullness of the number of Elect Jews which God had promised which he would save out if Israel.
(Isa 10:22 KJV) For though thy people Israel be as the sand of the sea, yet a remnant of them shall return: the consumption decreed shall overflow with righteousness. (Isa 37:32 KJV) For out of Jerusalem shall go forth a remnant, and they that escape out of mount Zion: the zeal of the LORD of hosts shall do this.

(Rev 21:13 KJV)
On the east three gates; on the north three gates; on the south three gates; and on the west three gates.

Each side had three gates which means we are looking at a perfectly constructed wall about the city. This is the same construction that Ezekiel saw because he also saw three gates on each side.  (Ezek.  48:30-35)

(Rev 21:14 KJV)
And the wall of the city had twelve foundations, and in them the names of the twelve apostles of the Lamb.

Now we are seeing that the wall had twelve foundations and in them the name of all the Apostles. Ancient cities had walls surrounding them which gave a sense of security to the citizens by helping keep out invaders. The wall here is built for the purpose of showing the universality of the body of Christ because it has twelve foundations and twelve gates into the city, three on each side with four sides. Four is the number of universality showing that God saved people out of every nation in the world. These twelve names represent the fullness of all the Gentiles which will be brought in to the Kingdom of God until the last day.

(Eph 2:19-22 KJV) Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God; {20} And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone; {21} In whom all the building fitly framed together groweth unto an holy temple in the Lord: {22} In whom ye also are builded together for an habitation of God through the Spirit.

In the Ephesians passage we see that true Christians are called fellow citizens who are built upon the foundation of the Apostles and Prophets with Jesus Christ being the chief corner stone. Then we read that these building blocks, which are the true believers, are fit together. The words “fitly framed” means “being fitted together.” In verse 22, the words “builded together” carries with it the meaning of “are being built together.’ So all the believers in the world, whether Jew or Gentile, are being both fitted and built together until we attain the fullness of the body of Believers. We see this fullness in Rev. 21:14 with the twelve foundations which represent the fullness. Ephesians tells us that the body is being built and fit, and Revelation tells us that the body is completed.