Why does Grant become a teacher? What are some of the paradoxes of his position as a teacher?

A Lesson Before Dying takes place in Louisiana in 1948, where racism is prevalent and an innocent black boy, Jefferson, is sentenced to death. Our protagonist and narrator is Grant, a teacher in the community. Grant's aunt has asked him to visit Jefferson in jail to help him face death with bravery.
Grant's aunt is the one who helped him go to university to make a better life for himself. Grant ends up taking his anger out on his aunt:

Everything you sent me to school for, you’re stripping me of it . . . All the things you wanted me to escape by going to school. Years ago, Professor Antoine told me that if I stayed here, they were going to break me down to the nigger I was born to be. But he didn’t tell me that my aunt would help them do it.

Grant went to school so he could make something of himself. As a black man during this time period, that meant becoming a teacher:

I could never be a hero. I teach, but I don’t like teaching. I teach because it is the only thing that an educated black man can do in the South today. I don’t like it; I hate it. I don’t even like living here. I want to run away. I want to live for myself and for my woman and for nobody else. That is not a hero. A hero does for others.

Grant tells Jefferson he didn't become a teacher because of a passion for the profession. It just seemed like his best option.
Grant's position as a teacher is paradoxical because he is the one who ends up learning the lesson before dying. He learns from Jefferson, who is supposed to be his student. Grant starts off pessimistic, thinking that nothing will ever change. But the visits with Jefferson help him find hope and believe in change.

My eyes were closed before this moment, Jefferson. My eyes have been closed all my life. Yes, we all need you. Every last one of us.