There are two things in the natural world which make the life there, namely, heat and light; and there are two things in the spiritual world which make the life there, namely, love and faith. Heat in the natural world corresponds to love in the spiritual world, and light in the natural world corresponds to faith in the spiritual world. Hence it is that when spiritual heat or fire is mentioned, love is meant; and when spiritual light is mentioned, faith is meant. Moreover, love is actually the vital heat of man, for it is known that man grows warm from love; and faith is actually the light of man, for it can be known that man is illumined from faith.
The heat and light in the natural world arise from the sun of the world; but spiritual heat and light, or love and faith, arise from the sun of heaven. The sun of heaven is the Lord; the heat which comes from Him as a sun is love, and the light which comes from Him as a sun is faith. That the Lord is light is evident from these words in John: Jesus said, I am the light of the world, he that followeth Me shall not walk in darkness, but shall have the light of life (John 8:12); and that the Lord is a sun is evident in Matthew: When Jesus was transfigured, His face shone as the sun, and His garments became white as the light (Matt. 17:2).
From this correspondence it can also be known how the case is with faith and with love. Faith without love is like light without heat, as is the light of winter; and faith with love is like light with heat, as is the light of spring. That in the light of spring each and all things grow and flower, is known; and also that in the light of winter all things become torpid and die. It is similar with faith and love.
from Arcana Coelestia, Sections 7082-7084