One of the advantages of have a limited first-person narrator is the opportunity for the reader to leanr along with the character. The first two chapters are Paul's acclamation to military action and his transition from school boy to soldier.
By chapter three, however, Paul is ready to begin forming relationships with the soldiers in his division. A number of his school-mates have either died or gone different directions, and his family is far away. The men in his division become both friends and family. As such, Paul begins to uncover the personalities of each one. As Paul becomes attached to each, so does the reader, making the death of each one more profound.
Remarque uses his limited narrator to manipulate the emotions of the reader, and in doing so, makes his anti-war message stronger.