Mundaka-1-1-4-tasmai sa

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

Com.—Angiras said to Saunaka. What did he say? (He said) that there were two sorts of knowledge to he known. So indeed, do those who know the import of the Vedas and who see the absolute truth, say what these two sorts are; he says: Para is the knowledge of the Paramatman and Apara is that which deals with the means and the results of good and bad actions. It may be asked how, having to say what it was that Saunaka asked about in the question—“What being known one becomes omniscient,’ Angiras stated what he was not asked about, by the passage “there are two sorts of knowledge, etc.” This is no fault; for the reply requires this order of statement. Apara vidya is ignorance and that ought to be dispelled. When what is known is Apara vidya, i.e., the subject of ignorance, nothing can be known as it is. The rule is that after thus refuting the faulty theory, the true conclusion should be stated.

Links
Various resources on the Mundakopanishad
Upanishad Series – Mundakopanishad Commentary by Swami Chinmayananda