"The spiritual master is addressed as 'Prabhupada' because he is a completely self-realized soul. The word pada means 'position' and Prabhupada indicates that he is given the position of prabhu, or the Supreme Personality of Godhead, for he acts on behalf of the Supreme Personality of Godhead. Unless one is a prabhu, or controller of the senses, he cannot act as spiritual master, who is authorized by the supreme prabhu, or Lord Krishna."
(Srimad-Bhagavatam, 4.23.18, Purport)
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