PHILADELPHIA — Imagine walking down a dirt pathway towards a bright, clean building in rural upstate New York. The windows are shutterless, neatly spaced rectangles; the roof is softly arched; and the walls are rattling with the screams, shouts, and stomps of dozens of people inside. You’ve arrived at the Second Meetinghouse of Mount Lebanon, the beating heart of a tiny, celibate, egalitarian, pacifist Christian sect: the United Society of Belie…