As members of St. Catherine of Siena, a parish here in the wealthy Northern Virginia suburb of Great Falls, the Santorums are immersed in a community where large families are not uncommon and many mothers leave behind careers to dedicate themselves to child-rearing, as Mrs. Santorum has. Mr. Santorum has been on the church roster as a lector, reading Scripture from the pulpit.

The parish is known for its Washington luminaries — Justice Antonin Scalia of the Supreme Court is a member — as well as its spiritual ardor. Mass is offered in Latin every Sunday at noon — most parishes have Mass only in English — and each Wednesday parishioners take turns praying nonstop for 24 hours before a consecrated communion wafer, a demanding practice known as Eucharistic adoration.

Image Mr. Santorum with his wife, Karen, and their family while announcing his bid for president last June in Pennsylvania. Credit... Stephen Crowley/The New York Times

The Santorum campaign did not respond to interview requests about the couple’s beliefs, and their pastors declined to comment. But friends say Mr. Santorum believes he is in a “moment of testing” and feels “a calling to be faithful,” regardless of whether he wins the nomination. One friend, Frank Schoeneman, sees Mr. Santorum as carrying out a vow he made to live a life that would make Gabriel, the child he lost, proud.

“Rick found himself in his faith, and he found himself in Karen,” said Mr. Schoeneman, who has known Mr. Santorum for more than 20 years. “He isn’t like one of these born-again people where you get hit in the head by some televangelist and you suddenly see the light. It’s been an evolution. He’s always been a Catholic and he’s always been faithful, but he’s never been at this level of faith.”

The Family Fold

Church on Sunday was a way of life in Butler, the western Pennsylvania town where Mr. Santorum grew up. But by the time he met his future wife, sports and politics were at the center of his world. He was working in Pittsburgh at the prestigious Kirkpatrick & Lockhart law firm and recruited Ms. Garver, then a University of Pittsburgh law student, for a summer internship.

Fair-skinned and auburn-haired, she was from a Pittsburgh family of 11 children, some of whom followed their father’s path into medicine. Dr. Garver was well known in Pittsburgh for a practice that included prenatal testing.