Remarque is able to use the contrasts between what could be or what was hoped to be and the grim reality of what is to illuminate the condition of war that young soldiers in World War I had to endure. In being able to do so, Remarque brings out the fundamental sadness in war.
Consider this use of contrast in Chapter 6 as an example of how themes are illuminated. The contrast of beauty, happiness, hope, and love to the condition of horror, sadness, hopelessness, and hate is seen in Paul's reflection of his past while on patrol. In a setting where rats battle men for food and a condition in which finding sustenance is near impossible, reducing humans to animals, Paul engages in a reflection of the past. Immersed in the midst of the horrors and destitution of war, Paul's memory of the past enables transcendence, if only for a moment. The lush greenery of his memory is in contrast to the desolation of the front. The beauty and joy of the past is forever lost to Paul and his comrades: "We are forlorn like children, and experienced like old men...we are lost.” The contrast between children and old men is poignant as it reflects the youth robbed from these soldiers as a result of war. Remarque is able to do this at different points in the novel, contrasting, for example, the patriotic fervor with which so many soldiers entered the war only to be confronted with the emptiness experienced while fighting it. The use of contrast helps to bring out what could have been in the face of what is.
Such a contrast helps to bring out the pain of war. It helps to illuminate a theme such as individual and machine, in which the contrast to a time in the past shows how the solider, used as a killing machinery and an instrument of death by those in the position of political power, used to be a human being, filled with love and hope. It also helps to enhance the theme of alienation, showing how the soldier is alienated between what beauty and glory existed in the past to the hopelessness and despair facing the soldier now.