Smith was a religious, Christian man. His notion of monads included contextual references to God. He believed that God controls the harmony of life through these monads.
The essay then goes on to discuss these monads in a Christian context. Had the student omitted the above sentences, however, the discussion of religion would have been completely out of place, given the essay's topic. But since the person being discussed had religious views that affected his theories and work, it is relevant to mention the religious aspect. Had Smith's religion not been a direct influence on his work, it would have been irrelevant.
Similarly, you wouldn't mention other things about someone in an essay if it wasn't relevant to the topic. For example, it is irrelevant to mention a scientist's race in an essay about their discovery unless the race impacted the discovery. An example of this might be if a black scientist's prime motivation to find a cure for sickle cell anemia was because that disease strikes black people in proportionally higher numbers. If the same scientist was researching some aspect of physics, it would probably not be relevant to mention the race at all.