Putnam and Campbell are quantitative, liberal, and upbeat; Hunter is qualitative, conservative and conflicted. But both books come around to a similar argument: this month’s ubiquitous carols and crèches notwithstanding, believing Christians are no longer what they once were — an overwhelming majority in a self-consciously Christian nation. The question is whether they can become a creative and attractive minority in a different sort of culture, where they’re competing not only with rival faiths but with a host of pseudo-Christian spiritualities, and where the idea of a single religious truth seems increasingly passé. Or to put it another way, Christians need to find a way to thrive in a society that looks less and less like any sort of Christendom — and more and more like the diverse and complicated Roman Empire where their religion had its beginning, 2,000 years ago this week.