Possibly "Good" songs and "Friday" songs? I'm not sure... I think a religious-themed set would be out of the question.
I would love a "Jesus Rock" set, actually, since most of it would be from the '70s.
How about a set of comeback songs?
Bobby Darin, "If I Were a Carpenter"
Cher, "I Found Someone" or "Believe"
Santana, "Smooth" (sorry)
Elvis, "If I Can Dream"
Ben E. King, "Supernatural Thing"
Jackie Wilson, "Whispers (Gettin' Louder)"
James Brown, "Living in America"
Aretha Franklin, "Freeway of Love" (or "Jump to It," I suppose)
Frankie Valli, "My Eyes Adored You"
Gary U.S. Bonds, "This Little Girl"