This quote comes on page 65 in the novel.
Salva has experienced horrible events so far. His uncle has been killed and buried just prior to this, and he is walking on in hopes of finding refuge at a sanctuary city. Looters had arrived at their camp and stolen everything they had, including food and clothes. Salva, being a child, did not have his clothes stolen because they would be too small for the looters—but they tied up his uncle and ended up shooting him dead.
After the group buries Salva's uncle, they begin marching on, and Salva is hungry, upset that they had lost their food and clothes, and distraught at his uncle's death. But, knowing the urgency and the necessity to reach safety, he is strengthened with resolve and marches on.