We have to understand the Babylonian Exile from the Old Testament in order to understand the Heavenly Jerusalem.
The entire description of the Heavenly Jerusalem is a reference back to the book of prophet Ezekiel, chapters 40 to 48, but especially chapters 47 and 48. Ezekiel was a prophet who operated during the Babylonian exile, when the jews were taken out of Israel by their captors and the temple had been destroyed.
At the time of Jesus, only two of the twelve tribes existed. About 580 years prior to Jesus, the Babylonians conquered Israel, destroyed the Temple in Jerusalem, tore down the city, and deported all twelve tribes to Babylon. Seventy years later only two of the tribes returned - Judah and Benjamin. The rest of the tribes, ten of them, had taken on the language, diet, customs and worship of their captors, were dispersed into the surrounding lands, and for all intents and purposes never seen again. Small remnants and pockets of their descendants remaind here and there, but they were effectively gone and never returned.
We also have to understand what Jewish belief was about the Messiah at the time of Jesus in post-exile Israel with ten of the twelve tribes gone into oblivion.
Jewish belief was that the messiah would be a new Moses who would institute a new exodus. The new exodus would not only be a physical exodus but a spiritual exodus as well, an exodus from sin and suffering.
About eight days after he said this, he took Peter, John, and James and went up the mountain to pray. While he was praying his face changed in appearance and his clothing became dazzling white. And behold, two men were conversing with him, Moses and Elijah, who appeared in glory and spoke of his exodus that he was going to accomplish in Jerusalem. (Luke 9:28-31)
It is easy to miss the fact that when Jesus speaks with Moses and Elijah on the mountain, they are having a conversation about a
new exodus which Jesus was to acomplish
in Jerusalem. It is easy to be distracted by the radical transfiguration of Jesus, and easy to miss the fact that the transformation of Jesus was a forshadowing of the transformation of the whole world.
The belief at the time of Jesus was that as part of the new exodus, the manna from heaven would return - and it did in the form of the Eucharist. And as part of the new exodus which would be led by the new Moses, the land itself would be transformed, including the Holy city of Jerusalem. Jerusalem would be transformed and God would dwell with man as he did with Adam and Eve in the garden of Eden.
Then I saw a new heaven and a new earth. The former heaven and the former earth had passed away, and the sea was no more. I also saw the holy city, a new Jerusalem coming down out of heaven from God, prepared as a bride adorned for her husband. (Revelation 21:1-2)
Belief at the time of Jesus was that the messiah, would institute a return of the ten lost tribes as part of the new exodus. He would also bring non-Jews into covenant relationship with God.
The messiah as the new Moses, the new exile, and the return of the ten lost tribes is the context in which we have to read Revelation 21. The reference to the foundations, walls and gates is, a reference back to the prophesy of Ezekiel.
the gates are named after the tribes of Israel—on the north, three gates: the gate of Reuben, one; the gate of Judah, one; and the gate of Levi, one. On the east side, measuring forty-five hundred cubits, three gates: the gate of Joseph, one; the gate of Benjamin, one; and the gate of Dan, one. On the south side, measuring forty-five hundred cubits, three gates: the gate of Simeon, one; the gate of Issachar, one; and the gate of Zebulun, one. On the west side, measuring forty-five hundred cubits, three gates: the gate of Gad, one; the gate of Asher, one; and the gate of Naphtali, one. The circuit of the city shall be eighteen thousand cubits. From now on the name of the city is “The LORD is there.” (Ezekiel 48:31-35)
Ezekiel describes a city with twelve gates, each gate named after one of the tribes of Israel. The entire passage in Revelation is a reference back the book of Ezekiel…
In a divine vision he brought me to the land of Israel, where he set me down on a very high mountain. In front of me, there was something like a city built on it. (Ezekiel 40:42)
***He took me in spirit to a great, high mountain and showed me the holy city Jerusalem coming down out of heaven from God. *
(Revelation 21:10)
Almost a perfect match. There is a measuring rod in both Ezekiel and Revelation, an innner and outer court in both books, a stream, a holy city on a mountain, and on and on an on.
Ezekiel 47 and 48 are definitely worth reading. Take a look at the
last line of the Book of Ezekiel and compare it to
Revelation 21:3.
Ezekiel is prophesying to the exiled jews that the temple would eventually be rebuilt in Jerusalem and that the Jews would return, but we know that only two of the ten tribes actually returned. John is using the prophet Ezekiel’s imagery to describe the eventual transformation of the whole world - including the ressurection of the dead - and much to the point of the question in the original post, to describe a reunification of the twelve tribes of Israel.
-Tim-