The sentence that develops the theme that a soldier often must harm other people to protect oneself is:
"The duty of the soldier was plain: the man must be shot dead from ambush—without warning, without a moment's spiritual preparation, with never so much as an unspoken prayer, he must be sent to his account."
This sentence emphasizes the harsh reality that a soldier is required to take lethal action without hesitation to safeguard himself and his comrades.