In what way is the intention of "Dulce et Decorum Est" to explore the human spirit?
Well, for one thing, this is anything but idealized and romanticized. There is none of the element of the supernatural here...no heros who fly in and rescue the guy flung in the back of the wagon with his eyes writhing and the blood frothing. UGH.
The poem explores the reality of war. How it really is...not what the propaganda tells you it is so that you will puff yourself up with pride and go marching off in a fancy uniform to be blown to bits.
Owen is one of the trench poets who wrote about the filth and the stench they lived in. They wrote about the death and the fear and the tears. This was not the popular way to write about war and battles then...not like today where there is no covering it up to protect the feelings of loved ones. With the advent of TV and movies, nothing is held back anymore.
The poem is about real life and death. The reality of living through it and being afraid you won't. Watching your friends die and hoping you won't be next...feeling guilty that you are still alive when he isn't. Being angry at the government for putting you there and the officers for making the orders you have to follow even if you don't want to do it. Afraid that when the time comes to pull the trigger, you won't be able to do it.
It's all the emotions we suffer as humans wrapped up into a nice, neat little ball of a poem.