The Major in "In Another Country" is a man of self-restraint. How could this personality trait of his help to enhance the pathos in the story?
In a big way! Hemingway is like a triple threat: He entertains, persuades and informs in his stories. As a war journalist he has placed a watchful eye on the personalities of the many soldiers he had observed, and made them his characters.
The pathos of this story is the ironies of war, life, fate, and personality. The personality of the Major is quite rich: He is kind of like a little Italian Napoleon with a penchant for order and control, and even the little things are a big deal to him.
Looking carefully, we notice how these are innuendos for mockery but at the same time they are important puzzle pieces that give the story its ironic pathos: No matter how much on top of life you think you are, fate will always be watching from the back burner to slip the rug from off your feet. Men fall. That was the Major's tragedy. Sadly, his fall was not due to the things that he could control, but due to the things that he couldn't. Disease, his wife, her life, and her fate.
This is why his personality adds weight and meaning to the pathos of the story.