It's probably a form of punishment for something he did or it's part of the "teaching" that he is sacrifice, some people use violence to make them understand and have them more docile so they don't resist
I feel like he might have done something wrong during his sacrifice lessons, cause they were also reciting the past and trying to say how grateful he should be for being chosen. It’s probs to show how hard life of being a sacrifice is.
The flashback scene is very confusing