The neighborhood fitness center where I have worked out for years closed down last month, and I had to join a new gym. The former place was a warm, friendly facility, patronized by older folks who liked to socialize while they worked out. We hardly ever broke a sweat. The new gym is a hard-core facility filled with serious men and women, earnestly invested in building better bodies. I watch these people strain and toil. Their bodies look strong, but I wonder if their hearts are being strengthened with grace.

Physiologically, the heart is a muscle—the muscle that keeps the other…