My instinct tells me "purpose" is maybe the enemy of a good personal essay. In my own experience, I'm always lost and wandering and searching - where am I? how'd I get in this mess? what's the point? - right through to the final draft, and sometimes even beyond that - baffled and defeated still, confused as to purpose long after the thing's in print. I never really have a guiding purpose or a point, not at the outset, anyway. It's like life: It's all discovered en route.