Question

What does Hemingway’s indirect characterization of the narrator reveal

Answer 1

The narrator tends to sponsor those who do not agree with him.

The narrator agrees with Passini although he does not admit it, the narrator also admits that the war is cruel, unjust and that it can not be avoided and, finally, the narrator does not have much patience to oppose the reasoning.

Answer 2

It reveals that the narrator recognizes that war is cruel, unjust, and inescapable. 
hope this helped!