In the Word, “light” in the highest sense represents Divine Truth: knowledge, ideas, understanding that come to us from the Lord. In lesser degrees -- the light of a lamp, the light of the moon and so forth -- it represents lower levels of truth, ideas and understanding drawn from more earthly sources. Also, the sun in the Word represents the Lord, with its heat representing the divine love and its light representing the divine wisdom. That wisdom flows into our minds and enters our lives in the form of truth -- things we can know and ponder that lead us and help us to be good people. This connection between light and thought is one of many spiritual/natural relationships that's embedded in our common language. People “see the light” when they understand something; we try to “shed some light” by bringing new thoughts to a difficult question; people are “enlightened” when they get new information or a more complete understanding of something. And a light bulb in a cartoon represents an idea!

920. 21:24 And the nations that are saved shall walk in its light. This symbolically means that all those people who live a good life and believe in the Lord will live in the New Church in accordance with Divine truths and will see those truths inwardly in themselves as the eye sees its objects.

The nations symbolize people who live a good life, and also people who live an evil life (no. 483). Here they symbolize people who live a good life and believe in the Lord, because they are called nations that are saved. To walk in light means, symbolically, to live in accordance with Divine truths and to see them inwardly in oneself as the eye sees objects. For the objects of spiritual sight, which are those of the inner intellect, are spiritual truths, and people who possess that intellect see them in a manner analogous to the way the eyes see natural objects. The light here symbolizes a perception of Divine truth from an inner enlightenment in those people from the Lord (no. 796), and to walk symbolizes to live (no. 167). From this it is apparent that to walk in the light of the New Jerusalem symbolically means to perceive and see Divine truths from an inner enlightenment and to live in accordance with them.

[2] But we need to illustrate this, because people do not know who are meant by the nations here, and by the kings mentioned next in this verse. The nations symbolize people who are impelled by the goodness of love received from the Lord, a goodness we call celestial goodness; and kings symbolize people who are impelled by truths of wisdom springing from a spiritual goodness received from the Lord, as we will see in the next number. People impelled by a celestial goodness from the Lord all have Divine truths engraved on their life. Therefore they walk, that is to say, live, uprightly in accordance with them, and they also see them inwardly in themselves, as the eye sees its objects. On this subject, see what we said in nos. 120-123 above.

All of the heavens have been distinguished into two kingdoms: the celestial kingdom and the spiritual kingdom. The goodness of the celestial kingdom we call celestial goodness, which is the goodness of love for the Lord, and the goodness of the spiritual kingdom we call spiritual goodness, and it is the goodness of wisdom, which in its essence is truth. Regarding these two kingdoms, see nos. 647, 725, 854 above.

[3] It is the same with the church, and those people are celestial there who live in accordance with the precepts of justice because they are Divine laws, as a civic-minded person lives in accordance with the precepts of justice because they are civil laws. But the difference between them is that, by his living in accordance with those precepts or laws, the celestial person is a citizen of heaven, to the extent that he inwardly regards civil laws that are laws of justice as also Divine laws.

Those people who are here symbolized by the nations, who have, as we said, Divine truths engraved on them, are the people meant in Jeremiah:

I will put My law in the midst of them and write it on their hearts..., and no more shall anyone teach his companion or anyone his brother, saying, "Know Jehovah," for they all shall know Me, from the least of them to the greatest of them... (Jeremiah 31:33-34)