Why was Stevens blunt when telling his father of his revised duties?

Stevens takes his job seriously, as does his father. After his father's fall, he finds it necessary to explain his new duties as professionally as possible. His manner was cold and matter-of-fact, a demeanor he learned from his father, and one that he aspired to. In the end, Stevens' father was proud of his son's actions. The respect between the two, father and son, is impressive.