The twelve-syllable (dvadashakshara) mantra of Vishnu-Krishna — the mantra of the Srimad Bhagavata itself, given to Dhruva by Narada, and beloved across all Vaishnava traditions.
Bhagavan is the possessor of the six opulences in full — strength, fame, wealth, knowledge, beauty and renunciation. “Namo bhagavate” salutes the Lord as that complete whole.
Source: Srimad Bhagavata (invocation) — Puranic tradition. Regional versions may vary — this text follows the version most widely used in community worship.