How does Paul change is All quiet on the western front, physically, mentally, and spirituality?

Paul looses his innocence in the war. He goes into the war a boy and comes out a man, his youth is lost. Paul's only family becomes his brothers in arms. He feels like a stranger in his own village, even with his own family. Paul understands how to survive in the trenches but little about civilian life. Paul becomes tough as nails but feels he lost his youth. By the end of the novel Paul is a man and a soldier but realizes that , come peace time, he will be lost.

"Had we returned home in 1916, out of the suffering and the strength of our experiences we might have unleashed a storm. Now if we go back we will be weary, broken, burnt out, rootless, and without hope. We will not be able to find our way any more."