Of the four Vedas, the Sama Veda is the Veda of music — its mantras are sung, not merely recited. Krishna identifies Himself with it, perhaps because melody reaches the heart more directly than prose ever can. Among the gods, He is Indra — their king and protector.
The most striking line in this shloka comes at the end: among beings, I am consciousness. Chetana — the quality of being aware, of knowing, of perceiving. Every creature's ability to sense and understand — that awareness itself is the divine. Not the body. Not the breath. The knowing behind the knowing.