The great question posed by the Upanishads is “by knowing what does all this that is become known?” The Upanishads in general focus on finding the key to our life and purpose, the core knowledge which illuminates everything we think, we feel, we do and we experience. The Mundaka Upanishad raises this question in the 3rd verse and provides the basis for the answer in the 4th verse.
Chapter One: Section 1, Verses 3-4: “Shaunaka, the great house-lord, came to Angiras in the due way of the disciple and asked of him, ‘Lord, by knowing what does all this that is become known?’ To him thus spoke Angiras: Twofold is the knowledge that must be known of which the knowers of the Brahman tell, the higher and the lower knowledge.”
There are several things to note in these verses. First, the Upanishad clearly indicates that the knowledge is not to be restricted to renunciates or scholars by bringing it to a wealthy householder, someone clearly immersed in the dealings of the external world. Second, there is obviously a respectful poise taken by this man of the world to the teacher, as he approaches “in the due way of the disciple”. This implies an open-minded and sincere seeking on his part, and acknowledges that knowledge is passed on through the guru-disciple relationship. This householder then raises the timeless question as to the core knowledge that is at the heart of the Upanishadic teaching. Interesting to note is the fact that the sage responds by describing both a higher and a lower knowledge. The higher knowledge represents the knowledge of Brahman; the lower, the knowledge of the world and its manifestation.
Sri Aurobindo, The Upanishads, Mundaka Upanishad, pp. 193-210