This requires depth, however…
You can rehearse until you’ve lost the feeling in your genitalia, but unless the Actors understand and have integrated the characters, the performance will never be better than memorized lines. The Director must work with them to help them understand the characters.
The relationship between the Actor and the Character, however, is not simply one direction. Every Actor brings themselves to the Character, and between the two of them, they’ll make something you might never have expected.
Ordinarily, I would assume between the Director and the Writer, they’ve figured out the characters, but I’ve been on projects where neither seemed to understand who the characters are. It has sometimes been only the Actor that made that connection.