Generally Speaking, the universe is divided into two worlds, a spiritual one and a physical one. Angels and spirits are in the spiritual world, and we are in the physical world. These two worlds are exactly alike in outward appearances, so much alike that there is no way to tell them apart; but as to inner appearance, they are completely different. The very people who are in the spiritual world (who are called angels and spirits, as I have just said) are spiritual beings; and since they are spiritual beings, they think spiritually. On the other hand, we who are in the physical world are physical, so we think physically and talk physically. Spiritual thought and speech and physical thought and speech have nothing in common. We can see from this that the two worlds, the spiritual one and the physical one, are completely distinct from each other, so much so that there is no way for them to be in the same place.
Since these two worlds are so distinct, then it is necessary that there be two suns, one the source of everything spiritual and the other the source of everything physical. Further, since everything spiritual is alive in origin and everything physical is dead in origin, and the suns are the origins, it follows that the one sun is alive and the other dead, and that the sun that is actually dead was created by the Lord by means of the sun that is living.
from Divine Love and Wisdom, sections 163-164