Aristotle believed that ethical knowledge is not only a theoretical knowledge, but rather that a person must have "experience of the actions in life" and have been "brought up in fine habits" to become good (NE 1095a3 and b5). For a person to become virtuous, he can't simply study what virtue is, but must actually do virtuous things.
We are not studying in order to know what virtue is, but to become good, for otherwise there would be no profit in it. (NE II.2)