The two great themes of John Updike's fiction are sex and religion. For his male protagonists, religion functions mostly as a fence -- not to constrain their carnal hankerings, but to make the "grass" looks greener on the other side.
Toward the end of Villages, almost as a throwaway, Updike offers three "evidential arguments" for the truths of Christianity.
The first is our wish to live forever, "however tedious the actual experience of eternal consciousness might be." Updike is remarkably well informed about science (more so than any other major novelist I am aware of), so he knows that an innate longing for immortality is a natural Darwinian response to the fear of death. In any case, it is hard to see what is specifically Christian about wanting to live forever.
Second, there is our sensation that "something is amiss," that things are not quite what they should be. I can go along with him on this, and there's no need to bring natural selection into it. Once nature has endowed us with consciousness, intelligence, and self-reflection -- presumably for good Darwinian reasons -- it is inevitable that we will wonder if there's not more to the world than meets the eye. But again, there is nothing specifically Christian about this; what we are talking about here is part of any religious response to the world, including that of the religious naturalist.
Third, Updike notes that belief benefits the health: "An anxiety-relieving faith conduces to worldly efficiency and success." He's on solid ground here; many scientific studies indicate that believers tend to be healthier and more at peace with themselves than nonbelievers. This applies not only to Christians, but to New Age navel-gazers, Jews on kibbutzim, and Tibetan monks. Even Updike's nominally Christian protagonist, Owen Mackenzie, knows that marginally better health is a shabby reason to believe. He wakes at three in the morning churning with the same anxieties as those of us who live our lives without the benefit of faith.