I think an important yet subtle theme featured in 28 Days Later is religion. From the very beginning of the movie when Jim enters the church, Boyle seems to be bringing a comment on religion into the movie’s analysis. For example, he could be making a comment on religion’s futility by rendering it useless in a place of killing and death. The church in the beginning could be seen as a place of sanctuary for people attempting to escape infection, but it is instead filled with already-infected and/or dead bodies (even the Father!).
This comment remains evident in the film’s other less obvious portrayals of religion, like the non-diegetic playing of “Ave Maria” behind a couple of scenes, and Selena using the words “began the exodus” in her initial conversation with Jim. These scenes directly call back and reference Biblical material.
Furthermore, Boyle uses select objects in the film to symbolize Biblical content, as well. From the festive Christmas decorations hanging in Frank and Hannah’s flat to signify the presence of Christ, to the four horses galloping in the countryside the characters visit to possibly represent the Four Horsemen of the Apocalypse, to even the starting and ending group of three characters standing for the Holy Trinity, Boyle fills his movie with religious imagery down to the most imperceptible details.
But — if Boyle believes religion is futile, then why is his movie so saturated with religious imagery and references? Perhaps Boyle is instead commenting on God’s/religion’s impartial omnipotence. After all, in the beginning, the “Rage” disease is man-made and initially spread due to human error, and at the end of the movie there is no divine intervention or favor to save the characters from their plight. There is nothing divinely given or natural about the events of the apocalypse, yet you can find references God’s presence everywhere. What is Boyle attempting to convey?