Most profoundly, the physicality of a chorus differentiates it from an omniscient narrator. We must remember that early Tragic chorus was very musical. Upon their first entrance, during the parados, choral members entered the orchestra dancing and singing in unison; their tone and inflection dependent on the mood prior to their entrance. Also, their rôle, at times--though not always--is somewhat more poetic/musical then that of an omniscient narrator's. Take, for example, the perfectly balanced musical attributes of the strophe and antistrophe--sometimes followed by an epode-- which bisects the chorus (in a sense) and amplifies its musicality. An omniscient narrator usually does not appear as a physical character. There is much more to unpack in this question, I haven't enough time to truly give a rich answer. Please, pose some follow up questions!
