Begin by thinking about how Milkman, the protagonist, changes throughout the novel. He takes a journey that is both physical and spiritual. His view of the world, himself, and his heritage is stretched, challenged, and ultimately rearranged.
Before his journey, Milkman was basically an amoral character. His outspoken views to Guitar about freedom and justice were hollow because he had no basis for his beliefs. He gave up easily and used the people who loved him. It is not until he discovers "his people" and his personal history that he is able to see that the entire world doesn't revolve around him, but that he is a part of a family, a tradition, and a legend.
Milkman's spiritual journey of finding his roots enables him to find truth, know sacrifice, and understand that he is forever tied to others and that his actions do have an impact on those around him. In Hagar's case, his actions had a tragic impact. Milkman's journey allows him to grow as a moral being and reassess his place in the world and in his family. Milkman's journey began as a quest for earthly wealth, but as he discovered the people and places around him he became hungry for knowledge about his family's past and ultimately himself, which is worth more than a hundred pounds of gold.