Cicely Tyson and "Blessed Assurance" Sara Krulwich/The New York Times Cicely Tyson's rousing "Blessed Assurance" in the Broadway revival of "The Trip to Bountiful" has Condola Rashad, left, and others joining in. Not long after the curtain rises on the second act of "The Trip to Bountiful," the Broadway revival of the Horton Foote play at the Stephen Sondheim Theater, something unusual happens. Cicely Tyson, as Mrs. Carrie Watts, sits on a bus station bench in a small Texas town. She is on the run from her abusive daughter-in-law and henpecked son in Houston, desperate to see the family farm in Bountiful once more before she dies. Overcome with emotion, she begins singing an old Protestant hymn, "Blessed Assurance." From the first note, there's a palpable stirring among many of the black patrons in the audience, which the play, with its mostly black cast, draws in large numbers. When Ms. Tyson jumps to her feet, spreads her arms and picks up the volume, they start singing along. On some nights it's a muted accompaniment. On other nights, and especially at Sunday matinees, it's a full-throated chorus that rocks the theater. "I didn't realize they were doing it until someone remarked to me how incredible it was that the audience was joining in," Ms. Tyson said in a recent interview, referring to her preview performances. "I said, "Where?" I was so focused on what I was doing that I didn't hear it. After the play opened, on April 23, she began tuning in. "At that point, I was relaxed enough to let other things seep in," she said. It was absolutely thrilling. Thrilling but unexpected. Under normal circumstances the Broadway experience does not include audience participation, even when catchy songs from classic musicals are being performed. The "Blessed Assurance" phenomenon is peculiar, perhaps even unheard-of, but the hymn itself is something out of the ordinary. "It is almost as ubiquitous as "Amazing Grace," " said Anthony Heilbut, author of "The Gospel Sound: Good News and Bad Times." It's one of those low-church Protestant hymns central to fundamentalist worship, black and white. He cited classic versions recorded by greats like Clara Ward, Sister Rosetta Tharpe, Albertina Walker and Marion Williams. Country singers like Alan Jackson and Randy Travis have recorded the song. Several black audience members, interviewed after a recent performance, seemed surprised that anyone might not know the hymn. "A lot of people in the audience grew up with that song," said Michelle Crawford, who first sang it when she attended the Thessalonia Baptist Church in the Bronx as a child. Nobody had to put the words out there in front of anybody. They knew that song. The singalong, too, struck black audience members as unremarkable. "I chimed in," said Pinkey Headley, who sings the hymn at her Methodist church in Brooklyn. It's the natural thing to do. Denise Wells, a member of the Mount Zion Baptist Church in Jamaica, Queens, agreed. "It's an old Sunday song," she said. She put a hand over her heart and began declaiming the hymn's opening verse, nodding emphatically after each line: "Blessed assurance, Jesus is mine! O what a foretaste of glory divine! The hymn was written in 1873 by two white women, Fanny Crosby and Phoebe Knapp, both members of the John Street Methodist Episcopal Church in Manhattan. After being published in a Methodist monthly that year, "Blessed Assurance" reached a wide audience when the evangelist Dwight Moody made it a feature in his wildly popular religious crusades. It became a staple in black churches after being included in the 1921 Baptist hymnal "Gospel Pearls." Ms. Tyson needed no introduction to the hymn. "It was one of my mother's favorites," she said. That ranking counts for something. Like Carrie Watts in the play, Ms. Tyson's mother was a storehouse of hymns. "I don't remember any Sunday, when she was in the kitchen making family dinner, when she wasn't singing a hymn," Ms. Tyson said. A pew in the Abyssinian Baptist Church in Harlem has a plaque, endowed by Ms. Tyson, that reads, "To Mother - Blessed Assurance." The hymn was not in the original play, however. Foote, who died in 2009, added it to the screenplay for the 1985 film, with Geraldine Page in the lead role. "Blessed Assurance" had deep meaning for Foote. His mother played piano at a Methodist church; he sang the hymn often and his grandmother sang it to him. Michael Wilson, the play's director, kept it in as a nod to the film and to Foote's love of the song. It also served as a useful transition from one scene to the next and as a way to show off the singing talents of Ms. Tyson and Condola Rashad, in the role of Thelma, the country girl who befriends Carrie on her bus trip and joins her in singing the hymn. Although the production received mixed reviews, both actresses earned Tony nominations for their performances. "It was never intended to be this way," Mr. Wilson said, referring to the audience singalongs. In the early previews he noticed that when Ms. Tyson got up from the bench, in a spontaneous gesture, it triggered something in the audience. "I was moved by the moment," Ms. Tyson said. It lifted me. Mr. Wilson recalled, "I said, "Keep that." " Correction: May 29, 2013 An article on Tuesday about audience members" joining in when Cicely Tyson sings a hymn in the Broadway play "The Trip to Bountiful" referred incorrectly to the show's cast. There are a few white actors in it; it is not an all-black cast. Because of an editing error, an article on Tuesday about audience members" joining in when Cicely Tyson sings the hymn "Blessed Assurance" in the Broadway play "The Trip to Bountiful" referred incorrectly to previous productions. Earlier ones have had either all-black casts or mostly black casts; and at least one production, at the Cincinnati Playhouse in the Park, included the hymn. It is not the case that before this Broadway production the play was performed by only white actors and that no productions included a hymn.