"...And he carried me away in the Spirit to a great and high mountain, and showed me the great city, the holy Jerusalem, descending out of heaven from God.... Rev. 21:10)
The saints of God on the earth were, and are, citizens of that heavenly city. Those who are in Christ are being built into a holy habitation, ultimately this Heavenly Jerusalem:
"Now, therefore, you are no longer strangers and foreigners, but fellow citizens with the saints and members of the household of God, having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief corner stone, in whom the whole building, being joined together, grows into a holy temple in the Lord, in whom you also are being built together for a dwelling place of God in the Spirit." (Ephesians 2:19-22)
Those citizens were being defrauded, jailed, tortured and killed for their faith by Jerusalem's Judaic leaders, and by the powers of Rome.
The book of the Revelation is God's answer to the haunting question from those who had been killed for the sake of the word of God: "How long, O Lord, holy and true, until You judge and avenge our blood on those who dwell on the earth?" (Rev. 6:10)
Their city would emerge triumphant.