Responses

He is doing it for Dr. Seok’s own good. It was just said that the first master wanted to off Seok for suspecting him for working with rebels (heavy implication of what actually happened with Dr. Oh). Major heard that and then saw all the notes, so he decided to detain Dr. Seok and keep it down low. In his position, he is supposed to just straight up execute Dr. Seok, but he didn’t. He is doing it because he is afraid that Seokhwa will die if he doesn’t take action.
Small spoiler: the next few chapters are going to be rough, but now you know the reason
i actually do think major kwak is arresting him for dr seok’s own good. he’s plotting something YALL TRUSTTTTT