What do you think about the main theme of the story? the main purpose of the writer of the story, what he wants to covey?
I would say that the theme of this story is that war is pointless. War is pointless (in modern times) because the old things that made war have a point do not apply today.
Pirandello shows the pointlessness of war by the way in which the characters try to show enthusiasm about the war but are unable to. We see at the end of the story that even the man who was most pro-war didn't really mean it.
War is so terrible (WWI was a war that was much worse in terms of human cost than anything that went before) that the idea of going to war for your god or your country seems pointless now.