On my way into Lincoln Center Saturday night I saw a poster for a ballet company with a quote from a critic: “At this level, ballet is a belief system.” The sentence flashed back during Serenade, as a girl arched into a full arabesque, bounding across the floor. Serenade is an initiation, for performers and audiences alike, into a great mystery. For better or worse, this girl was becoming a believer, in an art form that goes beyond normal human experience. SAB’s performance was full of little flaws, but they didn’t matter, they even added to the spell. Here, in every sense, were human beings in the process of becoming angels, messengers of the divine.