Mantra 1

ॐ ब्रह्मा देवानां प्रथमः संबभूव विश्वस्य कर्ता भुवनस्य गोप्ता ।स ब्रह्मविद्यां सर्वविद्याप्रतिष्ठामथर्वाय ज्येष्ठपुत्राय प्राह ॥ १ ॥

PLATE IMUṆḌAKA I.I.1–2brahmavidyāthe knowledge of Brahmanbrahmāfirst among godsatharvanhis eldest sonaṅgirin ancient timessatyavahaof Bharadvājaaṅgirasasked by Śaunakasarvavidyāpratiṣṭhāthe ground on which every knowledge rests
The knowledge of Brahman reached Aṅgiras through a named chain of five, unchanged in the passing.Drawn as a chain because here the chain is the content — this is the only place in the corpus where that is true. What travels is written once, above, rather than repeated in every ring.

In plain words

Om. Brahmā, first and foremost among the devas, creator of the universe and guardian of the world, taught to Atharvan, his eldest son, Brahmavidyā—the knowledge of Brahman, the ground on which every form of knowledge rests.