Bereshit B: Chapter 36
"Let there be a firmament"

In order to give illumination, the light of the sun must be reflected off a physical object. This is the secret of the word Firmament. To create resistance and a circuit of energy, a burning light bulb requires a filament. Man requires a metaphysical filament - the firmament - to create resistance against the Left Column energy of our desire to receive, which is our Evil Inclination. This firmament or filament is our free will to resist the negative urges and desires of the ego. When we apply this resistance, we create a metaphysical circuit that generates spiritual Light.