Before killing his "enemy," the sniper was convinced of his mission's need. He is shown to be completely committed to the war effort.
O'Flaherty is very deliberate in describing how the sniper feels about himself and the war initially. He felt that that he and the war effort were one in the same: "His face was the face of a student, thin and ascetic, but his eyes had the cold gleam of the fanatic. They were deep and thoughtful, the eyes of a man who is used to looking at death." The language used reflects how the sniper believed in the conflict throughout his being. The "ascetic" description reflects a religious zeal toward the war effort. This is enhanced with his facial expressions reflecting "the cold gleam of the fanatic," or a believer. The fact that the sniper is "thin" shows how he has put aside eating in the name of his mission, an idea supported with the fact that "he had eaten nothing since morning." The sniper is "excited" about what he is going to do and what he feels it means.
These descriptions show that the sniper believes in the war effort. He commits himself entirely to it. For the sniper, there is a singular devotion to the cause, which makes him perfect to carry out the mission. It also makes him perfect in terms of experiencing the disillusionment that accompanies it, something evident with killing "the enemy."