Principal Upanishad · Atharvaveda
Mundaka Upanishad 3.2.9
The knower of Brahman becomes Brahman
ब्रह्म वेद ब्रह्मैव भवति।
One who knows Brahman becomes Brahman itself.
What this verse points to
The verse describes knowing that is not a matter of acquiring information about something separate. Knowing and being coincide, which is exactly what does not happen with ordinary knowledge.
For practice this rules out a whole approach. No quantity of reading about this will constitute the knowing the verse means, and the text is not being anti-intellectual when it says so — it distinguishes higher from lower knowledge carefully elsewhere.
Sit with it
Close the book before the sit. Whatever you understood intellectually, let the sit be the other kind of knowing.
About the Mundaka Upanishad
Distinguishes "lower knowledge" (the sciences, ritual, even the Vedas as texts) from "higher knowledge," by which the imperishable is directly known. It supplies the image of two birds on one tree — one eating the fruit, one watching.
References to this text are given as chapter.section.verse — here, 3.2.9.