You can buy anything online—including one man's eternal soul. It all began when Hemant Mehta, a 23-year-old graduate student and atheist living in Chicago, wanted to explore Christianity. Raised in Jainism, an Eastern religion, Mehta had never even entered a Christian church. He also wanted to write about his experiences and get feedback. So he auctioned his soul on eBay.

The sale offered the chance to "save" Mehta's soul, with one hour of church attendance for every bid of $10. But then Jim Henderson got involved, and the direction changed radically. Henderson, a former pastor, is director of Off the Map, an organization that aims to "reinvent evangelism for ordinary Christians." Rather than trying convert Mehta, Jim wanted Mehta's take on the church.

With a $504 bid (the money was donated to an atheist organization), Henderson won the auction and the two embarked on a joint venture.

Mehta agreed to visit 12 churches they selected together and write about his experiences on Henderson's ...