Daniel Wise invited a prominent Orthodox rabbi to a recent preview of “Soul Doctor,” the musical that Mr. Wise wrote about Shlomo Carlebach, the charismatic songwriting rabbi whose music has become the heart of many modern synagogue services. The show, which opens on Thursday at Circle in the Square, was still being tweaked, and because the rabbi, Shlomo Riskin, had known Carlebach, Mr. Wise wanted his opinion. As it turned out, Rabbi Riskin was impressed with the show’s star, Eric Anderson, a genial Californian who wears an untrimmed beard and has absorbed Carlebach’s moves and sound. Backstage, Rabbi Riskin complimented Mr. Anderson’s performance in phrases peppered with Hebrew. It was only when Rabbi Riskin left that Mr. Wise told him that Mr. Anderson is not Jewish.

For Mr. Wise, and for Carlebach’s daughter, the singer Neshama Carlebach, Mr. Anderson’s Christianity is decidedly a plus.

“He’s really the best parts of my father, as far as I can see,” said Ms. Carlebach, who became involved in the production early on (and may occasionally appear in it). “And I love that he’s not Jewish. I love that he’s from another world and has thrown himself into this, not just because it’s a great work opportunity, but because, as he’s said to me, he’s really inspired by who my father was.”

Carlebach, the son of a long line of rabbis, fled Europe as a teenager in 1938 and became a rabbi in New York. Intent on persuading young, secular Jews to return to the fold, he surfed the folk music boom of the early 1960s, as well as the peace-and-love philosophy of hippiedom, and built a devoted following through his catchy, memorably folksy melodies and prayer settings.