First Mundaka chapters 4 through 6

 To him he said: Two kinds of knowledge must be known-that is what the knowers of Brahman tell us. They are the Higher Knowledge and the lower knowledge. 

5 Of these two, the lower knowledge is the Rig-Veda, the Yagur-Veda, the Sama-Veda, the Atharva-Veda, siksha (phonetics), kalpa (rituals), vyakaranam (grammar), nirukta (etymology), chhandas (metre) and jyotis (astronomy); and the Higher Knowledge is that by which the Imperishable Brahman is attained. 

6 By means of the Higher Knowledge the wise behold everywhere Brahman, which otherwise cannot be seen or seized, which has no root or attributes, no eyes or ears, no hands or feet; which is eternal and omnipresent, all-pervading and extremely subtle; which is imperishable and the source of all beings.