Religion has long provided ample source material for Matt Stone and Trey Parker, best friends who nearly 15 years ago created "South Park," the animated television show about four boys—and a lot of dirty jokes. For that show, Mr. Stone and Mr. Parker have mined Judaism, Catholicism, Islam—and even atheism—to make audiences laugh. Now, the comedic writers have relocated from Los Angeles to New York to stage their first Broadway musical, "The Book of Mormon," which they wrote and directed with "Avenue Q" writer Robert Lopez.

The...