If ātman already is brahman, what is left for liberation to do?
Recently I started on Advaita Vedānta, and one idea has stopped me cold.
As I understand it, the claim is that the self (ātman) already is ultimate reality (brahman). "Tat tvam asi", you are that, as Uddālaka tells his son in the Chāndogya Upaniṣad. Liberation (mokṣa) is therefore not achieving something new; it's recognising what was always the case.
But then why does the tradition prescribe years of study, discipline and meditation? If I'm already free, what is all that practice for? And isn't there a danger that "you're already liberated" becomes an excuse to do nothing, which, frankly, is attractive to someone in my state?
I'd like an explanation from someone who knows Śaṅkara well.