What Upanishadic shrutis describe the guru as essential to brahmavidya?

The Upanishadic shrutis explicitly establish that approaching a realized guru is indispensable for attaining knowledge of Brahman. This principle is directly paralleled in Bhagwan Swaminarayan's teachings, which identify the manifest guru as the essential awakener of brahmavidya.

The Mundaka Upanishad mandates formal discipleship to a teacher established in the divine reality:

"Let him, in order to understand this, take fuel in his hand and approach a Guru who is learned and dwells entirely in Brahman." (Mundaka Upanishad 1.2.12)

The Akshar-Purushottam tradition mirrors this exactly. The Siddhant Karika names the guru's precise function as the awakener of brahmavidya:

"महन्तस्वामिनं नौमि ब्रह्मविद्याप्रबोधकम्। निर्वैरं परमं शान्तं कृपालुं मे गुरुं प्रियम्" (Siddhant Karika 33)

Both traditions converge: supreme knowledge is transmitted through the grace of a teacher firmly established in the ultimate truth, positioning the guru as a living conduit rather than a mere academic instructor.