You don't need to have a strong religious faith to enjoy the serene atmosphere of Cathedral of St. Luke and St. Paul. Check when the next mass starts or when you can go for a wander through.
You'll have sightseeing choices galore when visiting Downtown Charleston. Cathedral of St. Luke and St. Paul is an ideal place to begin here, but there are loads of other worthwhile places to explore. USS Yorktown, College of Charleston, and Charleston City Market are near the principal church and will top off your day nicely.