The Steppenwolf Theatre Company production of Branden Jacobs-Jenkins' sharp-as-a-tack new play, Purpose, brilliantly directed by Phylicia Rashad and opening tonight on Broadway at the Helen Hayes Theatre, frequently surpasses the stunning brilliance of last year's Tony-winning revival of the playwright's Appropriate. And that's saying a lot, given the well-earned accolades heaped upon that play.