Throughout P. D. James's novel, Theo shows a skeptical attitude towards science and religion. Early on, Theo observes, “Western science has been our god.” This statement presents neither science nor religion in a positive light. For Theo, both serve a similar purpose in that they each can provide rather superficial forms of comfort, warmth, and entertainment.
At the start, what Theo arguably advocates is confronting the present. Although he is a historian, Theo believes it’s best to live in the reality of now. As Theo says,
We can experience nothing but the present moment, live in no other second of time, and to understand this is as close as we can get to eternal life.
Yet the “eternal life” end to the above quote reveals that Theo is not totally against the idea of spirituality or some kind of religious afterlife. But for Theo, no religion has a monopoly one how to grapple with the prefixing meaning of life.
When Rolf and Theo debate religion, Theo tells Rolf that one “doesn’t have to be a Christian” to figure out how to best live their life. In fact, Theo tells Rolf a version of what he told the reader earlier on. He informs Rolf, “That once I was not and that now I am. That one day I shall no longer be." This is all Theo can truly be sure of.
However, when Theo and Miriam discuss God, Theo tells her, “I may not be religious but I know my Bible.” He then says, “If He wants belief He'd better provide some evidence.” This last quote suggests a combination of science and religion. If God wants Theo to believe that He cares, then God, like a scientist, better put forth some empirical data.
Of course, if one focuses solely on the ending, then it’s possible to argue that God has ultimately emerged as victorious since Theo performs an emotional baptism on the baby.