Cities are to be established by those who love God and reflect His triune glory and community. Cities are places where people can live in such a way that the blessings exceed the sum of the parts - relationally, economically, intellectually, because, as members of a body, we are able to accomplish so much more when we are together. In fact, we can only accomplish many (most) things when we are in community, when we are in cities.
God calls His people a holy city, the New Jerusalem. He establishes her to be a beacon to all the cities of the world. He does so lovingly, taking that which was a harlot and making her holy again. Only the blood-mercy of God can do that.
"And it shall come to pass that he who is left in Zion and remains in Jerusalem will be called holy - everyone who is recorded among the living in Jerusalem. When the Lord has washed away the filth of the daughters of Zion, and purged the blood of Jerusalem from her midst, by the spirit of judgment and by the spirit of burning..." Isaiah 4:3-4.