Zech. 2:1 And I lifted my eyes and saw, and behold, a man with a measuring line in his hand! 2 Then I said, “Where are you going?” And he said to me, “To measure Jerusalem, to see what is its width and what is its length.” 3 And behold, the angel who talked with me came forward, and another angel came forward to meet him 4 and said to him, “Run, say to that young man, ‘Jerusalem shall be inhabited as villages without walls, because of the multitude of people and livestock in it. 5 And I will be to her a wall of fire all around, declares the LORD, and I will be the glory in her midst.’”
When I think of the power and prosperity of a city, I very rarely think of God as being that city's defence and source of all that is good in her. That is a mistake! If the LORD is a wall of fire around a city, it is impregnable. It's a striking description of Jerusalem as it will be—the heavenly Jerusalem, of which all Christians are citizens.
The prophecy of Zechariah finds its fulfilment in the Revelation to John:
Rev. 21:22 And I saw no temple in the city, for its temple is the Lord God the Almighty and the Lamb. 23 And the city has no need of sun or moon to shine on it, for the glory of God gives it light, and its lamp is the Lamb. 24 By its light will the nations walk, and the kings of the earth will bring their glory into it, 25 and its gates will never be shut by day—and there will be no night there. 26 They will bring into it the glory and the honor of the nations. 27 But nothing unclean will ever enter it, nor anyone who does what is detestable or false, but only those who are written in the Lamb’s book of life.
The reason Jerusalem is filled to overflowing is because the people of the nations have been drawn in to her by the light of the glory of God.