Since Brahman has many limiting adjuncts, each with diverse forms, a meditation on the same Brahman as possessed of the limiting adjunct of the mind, is being enjoined.
Verse 5.6.1:
मनोमयोऽयं पुरुषो भाःसत्यस्तस्मिन्नन्तर्हृदये, यथा व्रीहिर्वा यवो वा; स एष सर्वस्य सर्वस्येशानः, सर्वस्याधिपतिः, सर्वमिदं प्रशास्ति यदिदं किञ्च ॥ २ ॥
इति षष्ठं ब्राह्मणम् ॥manomayo’yaṃ puruṣo bhāḥsatyastasminnantarhṛdaye, yathā vrīhirvā yavo vā; sa eṣa sarvasya sarvasyeśānaḥ, sarvasyādhipatiḥ, sarvamidaṃ praśāsti yadidaṃ kiñca || 1 ||
iti ṣaṣṭhaṃ brāhmaṇam ||1. This being identified with the mind and resplendent (is realised by the Yogins) within the heart like a grain of rice or barley. He is the lord of all, the ruler of all, and governs whatever there is.
This being identified with the mind, because he is perceived there; also he perceives through the mind; and resplendent, lit. having lustre as his real state or nature. Since the mind reveals everything, and he is identified with the mind, therefore he is resplendent, i.e. is realised by the Yogins—we must supply these words—within the heart like a grain of rice or barley in size. He is the lord of all things, which are but variations of him. Even with lordship, one may be under the sway of ministers etc., but he is not like that. What then is he? He is the ruler, independent protector, and governs whatever there is—the whole universe. The result of this meditation on Brahman identified with the mind is the attainment of identity with him as such, for the Brāhmaṇa says, ‘One becomes exactly as one meditates upon Him’ (Śatapatha Brāhmaṇa X. v. ii. 20).