The part that knows but chooses not to. So, what is the darkness. It is not the evil, it is not the devil. It is not sin. Darkness is the absence of light.
Darkness is the absence of shining.
If shining is a choice, then darkness is also a choice. You see, it requires a lot of energy to harbour resentments, hold on to hate, to be willing to unforgive, to be angry, to be jealous, to be envious, to distract yourself from your calling, to be unhappy, to be cruel, to be vindictive, to be hurtful, to be discontent with people, to be discontent with your finances, to be discontent with your life. It is your choice. You and only you have the power to make this choice to live in the light or in the dark. Often people have to hit the bottom of the barrel before they realize that they need to look at and rechoose the priorities in their life.