Besides the incredible brilliance of the city, there are these two more things that John draws our attention to. He tells us in verse 14, that the walls for the city have twelve foundation stones, and written (or engraved) on them are the names of the twelve apostles (one apostle on each stone I presume). We don’t know how the foundation stones are arranged, but we are told that each one is adorned, or studded, with a particular precious stone. Here is a list of the twelve precious stones: jasper, sapphire, chalcedony, emerald, sardonyx, sardius, chrysolite, beryl, topaz, chrysoprase, jacinth, amethyst.
I am sure that much has been written about these things, as there is a great deal of meaning attached them; however, I will mention only one thing. It is obvious to me that since the names of twelve apostles are engraved on the foundations, this confirms to us that God thinks very highly of the church, particularly the twelve apostles. They indeed are the foundation stones of the faith (Eph. 2:20).
Just as there are twelve foundation stones, there are also twelve gates, three on each wall (v. 12). And at each gate there is an angel standing guard; and written on the gates are the names of the twelve tribes of Israel—one tribe on each gate. This I believe shows us that the angels will be with us in heaven forever; and it also shows us the great importance of Israel in the city—that they will not be forgotten as a people or blended in with all other believers. No, they will always be a distinct and particular people.
Now the gates themselves are made of pearl—each gate of one pearl (v. 21). We are not told the dimensions of the gates, but I imagine that they are very huge and tall. These pearl gates are not like any you have ever seen. Some translations indicate that each gate is one single pearl, others express that each gate is made of one pearl.
Nonetheless, I think that the most important thing to consider here is not the hugeness or the beauty of the pearl, but the possible meaning. In this case I think the meaning is found in the formation of the pearl, for just as earthly pearls are formed in response to the irritation and wounding of oyster flesh, so these gigantic God-made pearls will remind us throughout eternity how that our sin has wounded Christ, and how He, to protect His honor, has wrapped us in the righteousness of Christ and made us beautiful and righteous.
The gates also represent the great strength of God to keep out sin and any ungodliness from the city; yet we know that that is merely a symbolic representation, for all sinners will have already been locked up in hell. Thus there will never be a possibility of that incursion.
At the same time, since the gates will never be shut, this tells us that all believers will be welcome to come and go, in and out of the city at any time. Thus for eternity we will be free to stay in the glorious city, or to roam the earth, or possibly to even explore the universe at our leisure.