There was no excuse for saying no: the pastor ordered his parishioners to have sex. Lots of sex.

When the staff at Relevant Church in Tampa, Florida, wanted to conduct a sermon series on relationships, they chose to focus on sex. The 30-Day Sex Challenge dared married couples to hop between the sheets—and non-marrieds to abstain—every day for a month.

Some church members, especially wives, reacted with skepticism. "At first the women thought this was all about sex," said lead pastor Paul Wirth, but he noted that most came around quickly. "This challenge no longer allowed men to come home from work and not help out around the house, not help out with the kids, and not meet his wife's needs—and then expect there to be fireworks in the bedroom," Wirth added.

But husbands, too, benefited from the challenge in ways that were more than physical. "My wife and I discovered that [the challenge] opens the door for communication into every aspect of our lives," one man said, "and ...