The evil inclination states its opinion in the left part of the heart, from the heart the desire ascends to the mind for contemplation.
Immediately upon its ascent to the brain it is challenged by the divine soul residing in the brain, which extends into the right part of the heart where the good inclination abides.
The final verdict rests with the arbitrator — the Holy One, blessed be He, who comes to the aid of the good inclination, enabling it to prevail over the evil inclination.
As our Sages say, “Man’s evil inclination gathers strength daily,…and if the Almighty did not help him he could not overcome his evil inclination.”
The help that Hashem grants him is the glow of divine light that illuminates his divine soul, that it may gain superiority and mastery over the folly of the “fool”, the evil inclination, paralleling the superiority of light over darkness.
(Tanya Chapter 13)