What are the gates and foundations of New Jerusalem?
New Jerusalem has a great high wall with twelve gates bearing the names of the twelve tribes of Israel, and twelve foundations bearing the names of the twelve apostles of the Lamb.
The holy city, New Jerusalem, is shown coming down out of heaven from God with a wall that is great and high. That wall has twelve gates, and at each gate stands an angel, with the names of the twelve tribes of the children of Israel written on them: three gates on the east, three on the north, three on the south, and three on the west.
The wall of the city also has twelve foundations, and on these foundations are written the names of the twelve apostles of the Lamb. An angel measured the city, its gates, and its wall with a golden reed, showing how carefully and purposefully this city has been established.
The city itself has the glory of God, shining like a precious stone, clear as crystal, and it is described as the Bride of Christ, the Lamb's wife. Its gates are never shut, for there is no night there, and only those written in the Lamb's book of life may enter; nothing that defiles or works abomination or makes a lie is allowed inside.
The scriptures
And he carried me away in the spirit to a great and high mountain, and shewed me that great city, the holy Jerusalem, descending out of heaven from God, Having the glory of God: and her light was like unto a stone most precious, even like a jasper stone, clear as crystal;
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: On the east three gates; on the north three gates; on the south three gates; and on the west three gates. And the wall of the city had twelve foundations, and in them the names of the twelve apostles of the Lamb. And he that talked with me had a golden reed to measure the city, and the gates thereof, and the wall thereof.
And the gates of it shall not be shut at all by day: for there shall be no night there. And they shall bring the glory and honour of the nations into it. And there shall in no wise enter into it any thing that defileth, neither whatsoever worketh abomination, or maketh a lie: but they which are written in the Lamb’s book of life.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.