He had observed the comings and goings of man from a distance and though humanity thought they grasped fair knowledge of His existence, their limited minds could only fathom glimpses of His omnipresence. Through the short span of time that constituted their existence, a mere five thousand years or so, they had bestowed so many names upon Him that He couldn't help but be amused at their feeble attempts to comprehend Him. They served their purpose though – they amused Him well enough.
But as He watched them repeat the same patterns of weakness and chase in vain after their various petty concerns, He grew bored with witnessing the same monotonous conflicts replayed in different banal permutations and decided to invent a new distraction to capture their imaginations. Since men seemed to require that their world be divided into a categorical good and evil, He would give them a new obsession to create a deeper schism amongst humanity. He would grant them both the power to destroy their world as well as the means to save it, and He would let them choose their own end. The strongest among them would wield this power and deliberate the outcome of their lesser peers. At the very least it would afford Him a few more centuries free from boredom. After that, if they proved to have outlived their usefulness, He would simply allow them to continue as the architects of their own demise. They wouldn't last much longer in any case.
Man appeared to have a penchant for weapons, war, and destruction so He decided that would be the nature of His instrument of discord. Fashioning two swords, one good, the other infused with malevolence, He hid them in opposite ends of the world and began to plant the seeds of their existence into the consciousness of its inhabitants. Now that the stage had been set, all that was left was to raise the curtains on its players and watch the chaos that would inevitably unfold.