The original question had to be edited down. I would suggest that the primary significance of the daydream is to bring to light how far off reality is from it. Paul's daydream brings to light the disconnect between what is being experienced in the war and what once was. Part of the daydream's significance is that it brings to light the collision between the ideals that set the war in motion and the reality that has confronted its participants: "We are forlorn like children, and experienced like old men...we are lost.” The lack of understanding in the severe disconnect between what is and what should have been as well as the fact that the soldiers were led astray, no different than children, is where Paul's reverie or daydream holds significance. The physical brutality and the gruesome nature of what is shown in the chapter is set against this dream, a conditional statement of hope and promise, in a barren world that has done enough to shatter such illusions. The vast amount of death and despair which surrounds the soldiers is in stark contrast to what Paul recalled as what once was, never to be again. It is here where I think that his daydream holds the greatest amount of significance in the chapter's development as well as the thematic understanding of the narrative.