I came across this question the other day and I wondered if you might want to explain this passage to me.
Revelation 3:12 Him that overcometh will I make a pillar in the Temple of My God, and he shall go no more out: and I will write upon him the Name of My God, and the name of the city of My God, which is New Jerusalem, which cometh down out of Heaven from My God: and I will write upon him My New Name."
This is an incredibly important text, that goes back to the O.T..
Isaiah 56– The promise of a New Name when the eunuchs would be brought into the house of God–See Acts 8 and the conversion of the eunuch!! How often we just gloss over the conversion of the eunuch, perhaps focusing on the fact that he was an Ethiopian, instead of him being a eunuch!! His nationality was not the point. His being a eunuch, emphasized in the Greek by being used 5 times, is the point, and shows us that Luke was trying to get his readers to see the fulfillment of Isaiah.
Isaiah 62–The New Name in the New Jerusalem, when God remarried Israel– see Matt. 22–Revelation 19–This time of the remarriage would be at the coming of the Lord with His reward (v. 11-12. But, fascinatingly, v. 11 is the verse that stands behind Jesus’ promise to come in judgment in the lifetime of his audience (Matthew 16:27-28).
Isaiah 65:13ff)– The New Name would be fully given when Old Covenant Israel would be destroyed, and God created a new people.
So, as Revelation 3 contains so many of these prophetic motifs and themes, Jesus was essentially saying that the church, the body of Christ was the fulfillment of those prophecies, and they were about to be consummated with the arrival of that New Jerusalem "coming down from God out of heaven." (Revelation 21:3). This is confirmed further by the fact that in Revelation 3:9f, Jesus quotes directly from Isaiah 60:14, another prophecy of the restoration of Israel, and applies it directly to the church!
This is really good stuff, when we see the consistent prophetic theme!
Hope this helps just a bit.