A. Why Mitzvah’s are referred to as light: Torah Or p. 81a-82a

In Scripture we find that Mitzvah’s are compared to candles. The reason for this is because just as when a candle is lit, its light fills the room, so too when one fulfills a Mitzvah it radiates a Divine light which is a ray of the Divine presence. This ray shines in the garden of Eden and is the source of the pleasure of the souls that abode there. This works as follows: When a Jew fulfills a command it arouses above that Hashem also fulfills that same command within the spiritual worlds. This fulfillment of Hashem elicits a Divine revelation within the spiritual world, and it is this elicited Divine revelation that serves as the source of the pleasure of the souls in the garden of Eden through them comprehending this Divine light.