An audience sits rapt in a darkened venue in Jerusalem as a guitar sounds plaintive notes that wind into chords. The crowd — men in knitted kippot, as well as black yarmulkes, fedoras, and some shtreimlach too — starts swaying as the chords build on each other and the melody takes a familiar shape. As the audience rises in one voice to take hold of it, the band picks up the cue and Shlomo Katz begins the lyrics, while everyone instinctively grabs his neighbors’ hands and joins the dance…