A. In the first two centuries [AD], men may kiss men, women women, but also you would have men and women kissing one another. In future centuries, there continued to be a debate over who should kiss whom. In later years, Christians will no longer have men and women kissing each other, but only men men, women women. [Christians had] debates on whether or not priests could kiss the laity, on whether you should kiss a non-Christian relative in the normal, everyday situation, even debates over whether Jews have a kiss or not.
A. In antiquity, a kiss on the lips was seen as transferring a little bit of one's spirit to the other person. You have a lot of early I kind of think of them almost as Greco-Roman Harlequin novels that speak of the kiss as this transfer of spirit. Christians modify it a bit, to suggest that when Christians kiss each other, they don't just exchange their own spirit, but also share a part of the Holy Spirit with one another. So the kiss is seen as a way to bind the community together.