That all this dancing is happening at a wedding — the only place we grown-ups ever get around to dancing anymore — adds to the performance’s piquancy. The story it tells is not just the story of Jill and Kevin — though obviously it’s their story too — but of the joy that every bride and groom (or bride and bride) (or groom and groom) has felt as they walked down the aisle. The audience — in the church, and 8 million strong and counting out in the world — feels it. Intentionally or not, as a piece of theater, Jill and Kevin’s big musical number is courtship in microcosm: wildness and improvisation giving way over the course of time to steady, comfortable companionship. A crowd of friends are there to back them up. Out of the storm of many, two.