Garry Wills writes in The Huffington Post:

Before the Easter Bunny nibbled its way onto sacred turf, Easter was a very serious business. In early Christian communities — in fourth century Milan, for instance — it was the day when, normally, all new Christians were baptized, and it was the deepest spiritual experience most of them would ever have. But the very things that impressed those “born again” in “saving waters” would probably upset modern people — things like their being stripped naked in church and then anointed with oil all over their body, or going naked into a pool where their heads would be held under water three times for “total immersion.”