President Barack Obama isn’t an overtly religious man. He and his family rarely attend church. He almost never elaborates in public about his own relationship to his Christian faith. But away from the public eye, his advisers say the president has nurtured a spirituality that’s served to help ground him during turbulent times. Every year on Aug. 4, the president’s birthday, Obama convenes a group of pastors by phone to receive their prayers for him for the year to come. During the most challenging of times, prayer circles are organized with prominent religious figures such as megachurch pastor Joel Hunter,...