The Words and Phrases of the Lotus Sūtra, fascicle 4, states: “It is said that a thief acquired the golden head of a Buddhist statue by uttering ‘Namu Buddha.’ How much more so for a wise man saying this. Venerable gods in the entire universe will not fail to help a wise man. Be diligent and don’t be lazy.”

This interpretation means that once upon a time there was a state in India where the gods in heaven were worshiped but Buddhism was not. A Buddhist temple was built there enshrining the King of Devils in the Sixth Heaven. As the head of this King’s statue was made of gold, a thief had been trying to steal it for years in vain. One day this thief sneaked into the temple and listened secretly to the Buddha’s sermon saying that “namu” means “to be surprised and awakened.” So, the thief chanted “Namu Buddha.” This enabled him to get hold of the head of the Buddhist statue that he had been trying to steal. Later he confessed it to an investigator. As a result, it is said, everyone in the state abandoned the gods in heaven and became a Buddhist. Surmising from this instance of a thief, even a sinner can be relieved of a great burden if one believes in the Three Treasures of Buddhism.

Dōjōjin Shugo-ji, Protective Deities for the Place of Practicing Buddhism, Writings of Nichiren Shōnin, Volume 6, Followers I, Pages 16