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
The Brahmavidyā that Brahmā declared to Atharvan, Atharvan taught in ancient times to Aṅgir. He taught it to Satyavaha of the Bharadvāja line, and Satyavaha Bharadvāja taught Aṅgiras the knowledge embracing the higher and the lower.