Most of us give little attention, other than winks and giggles, to the verses commanding us to "greet one another with a holy kiss." Mount Holyoke religion professor Michael Penn, however, has recently written an entire book on that early church practice: Kissing Christians: Ritual and Community in the Late Ancient Church (University of Pennsylvania Press, 2006).

Let's first define "ritual kissing." When did early Christians kiss and who kissed who?

Our earliest reference to the kiss is from the apostle Paul in 1 Thessalonians. He doesn't give us very many details, which suggests that it was already a well-established practice.

It's only decades later that other Christians give us more details. We discover that early Christians kissed each other in a variety of different rituals, as part of prayer, baptism, Eucharist, everyday greeting, martyrdom, and so forth. In the first two centuries, at least, not only did men kiss other men and women other women, but men and women kissed one another. And most often this was a kiss on the lips.

What did the kiss mean culturally in the broader Greco-Roman context?

The short answer is that it meant a heck of a lot of different things, just as it does in our own time period. We find everything from a romantic kiss to a familial kiss to a kiss between friends. One difference between us and the ancient world, however, is that then when people kissed, particularly on the lips, it was seen as an exchange of spirit. Sometimes Christians would take the contemporary cultural meaning wholesale, and other times they would modify it.

How did Christians modify the meaning of the kiss from what it was outside the church?

For example, often Paul spoke of Christians being brothers and sisters in Christ. So ...