This spiritual light of the Holy City would extend to the whole world of darkness: the nations of them that are saved shall walk in the light of it: and the kings of the earth do bring their glory and honor into it--21:24. This part of the vision represented the saved as having come from all nations, that the Jew and Gentile together should walk in the light of the gospel.
The language has its counterpart in the descriptions of Isaiah (chapters 2:2-5; and 62:1-2) which were the prophecies of the new Jerusalem of the new covenant which would include all nations. The prophet said: “ 0 house of Jacob, come ye, and let us walk in the light of the Lord.” This prophecy was made by Isaiah in connection with the establishment of the new institution on the top of the mountains, and the promulgation of the new law from Jerusalem. It is the same imagery in chapter 21:4 of this vision: “ And the nations of them which are saved shall walk in the light of it.” In the prophecy of Isa 62:1-4, the prophet declared that “ the Gentiles shall see thy righteousness, and all kings thy glory.” And in this vision the Seer said: “ And the kings of the earth do bring glory and honor into it.” It was the vision of all nations yielding to the influence of the gospel, as if the kings of the nations had brought the glory of their crowns and scepters and treasures into the kingdom of God and of Christ by the conversion of the people of the whole world. The vision here is the extension of chapter 11:15: The kingdoms of this world are become the kingdoms of our Lord, and of his Christ. All of these verses and visions referred to the universal expansion of Christianity in the spread of the gospel over all the world.