What were Aristotle's views on Moral Responsibility?

What does he mean when he says that 'so whether it is not by nature taht the end appears to each person in whatever way it does appear, but the person plays some role as well, or whether the end is fixed by nature, but virtue is voluntary because the good person does the remaining actions voluntarily, vice will be no less voluntary than virtue'? (in Nicomachean Ethicsm, book iii ch. 5)