Taittiriya Upanishad, Shikshavalli, Chapter Four begins with a prayer to Indra for illumination. Sri Aurobindo has provided two translations of this prayer of which this one is directly referenced by him in his introduction to the Upanishads:: “‘He who is the Bull of the Vedas of the universal form, he who was born in the sacred rhythms from the Immortal, — may Indra satisfy me through the intelligence. O God, may I become a vessel of the Immortal. May my body be full of vision and my tongue of sweetness, may I hear the much and vast with my ears. For thou art the sheath of Brahman covered over and hidden by the intelligence.” He mentions that this passage clearly breaks through the veil of outer coverings of the esoteric teachings and identifies Indra as the power of the divine mind.
Having invoked the powers of the divine mind, the teacher now requests the bodily capability and the material support required to sustain himself and the disciples, whom he also now calls forth to share in the illumination he has been vouchsafed.
The teacher recognises that the results are not something achieved through his own effort alone. “Thou art a river with a hundred branching streams, O Lord of Grace, in thee may I wash me clean.”
Sri M. P. Pandit notes: “It is the Divine Lord who is to bend and take up into Himself him who is striving to reach out to Him, who by dint of tapasya has arrived near his proximity but cannot go further without His Grace.” As Sri Aurobindo translates: “O Lord, thou art my neighbor, thou dwellest very near me. Come to me, be my light and sun.”
Some traditional commentators consider the verse to be construed somewhat differently, by indicating that the reference to the “bull of the hymns of Veda whose visible form is all this Universe” (as translated by Sri Aurobindo in his second translation of this section) refers to OM, which is the preeminent symbol of the creation and the epitome of the Vedas. The grammatical structure would tend to support the first approach as it appears to be an epithet of Indra, not a segue from one thought to the next.
In the end, the focus of this verse is clearly on the invocation of the higher powers of the mentality to illuminate the teacher and prepare him to receive and support sincere students who are ready to receive this illumination.