What do we learn in this novel?

It is not clear if this question is asking about what readers learn about characters over the course of the play or what readers learn as a result of seeing the play as a whole. One thing that we learn is that Hally really does not have a good relationship with his father. Hally's father is in the hospital, and Hally really does not want his dad to come home. This is shocking to audiences, but we eventually learn that Hally's dad is a deadbeat drunk of a father. During much of the play, it becomes quite clear to audiences that Sam has essentially been acting as young Hally's father for quite some time. They joke together about all kinds of things. Sam helps him with his homework, and they get into philosophical discussions of various kinds. Despite this apparently deep and rich relationship, audiences see that Hally does not see Sam as a father figure or as an equal. Hally spits in Sam's face, makes racist jokes, and demands to be called "Master Harold." The relationship is broken forever, and audiences learn the danger and consequences of lashing out in anger and saying something that might not be able to be taken back. Sam says the following:

If you make me say it once, I'll never call you anything else again. . . . You don't know all of what you've just done . . . Master Harold. It's not just that you've made me feel dirtier than I've ever been in my life . . . I mean, how do I wash off yours and your father's filth?