When most people think of the Pope, they envision him in gilded buildings at the Vatican or making appearances on a velvet-covered balcony, not attending a student concert conducted by Latin School band teacher Cynthia Gradek. But long before he was Pope Leo XIV, Robert Prevost was a crucial part of the St. Rita of Cascia community on Chicago’s Southwest Side, where Ms. Gradek first met him. St. Rita High School is run by the Augustinian Order, a Catholic church order devoted to education, evangelization, and pastoral care. In her 23 years of teaching at St. Rita, Ms. Gradek often attended mass run by the then-Father Prevost, who led the Midwest Augustinians at the time. “Whenever he would come back to town, he would do a mass for the entire school community, and he would talk about...