Why does David kill the magpie and what important life lessons does he learn from his experience?

In Chapter Two, David's grandfather gives him a pistol and bullets in case he runs into coyotes while he is out riding. Not accustomed to having a multi-shot gun, David looks to his parents for permission, and they agree, but stress that he’s only to shoot coyotes. David runs quickly to the stables, saddles up Nutty, and starts trotting through the countryside. He finds an area far enough from the house where he can’t be heard and plays around with the gun, sometimes shooting at the ground, sometimes aiming for objects. Most of the time he misses, but one time he shoots and kills a magpie. The kill sparks feelings of power, sadness, exhilaration, fear, and eventually calm in David. Killing the magpie releases a tension that was building in him because of Marie’s illness, his uncle’s sins, and his parent’s arguing. As he buries the magpie, he realizes that strange, unthought-of connections like sex and death, lust and violence, and desire and degradation exist even in the purest of hearts.