What is the importance of the teacher in beloved?

The following excerpt in from gradesaver;

"Schoolteacher was a cruel and sadistic master, interested in ways to break the wills of his slaves. He conducted a pseudo-scientific study of the slaves, treating them in his study the way a biologist treats lab animals. His nephews held Sethe down and stole her milk while schoolteacher took notes. When it was discovered that Sethe told Mrs. Garner what they had done, schoolteacher had one of his nephews whip Sethe, giving her the distinctive scars on her back."