(Click to enlarge photo of His Divine Grace Srila Prabhupada)
"Without being empowered by the direct potency of Lord Kṛṣṇa to fulfill His desire and without being specifically favored by the Lord, no human being can become the spiritual master of the whole world. He certainly cannot succeed by mental concoction, which is not meant for devotees or religious people. Only an empowered personality can distribute the holy name of the Lord and enjoin all fallen souls to worship Kṛṣṇa. By distributing the holy name of the Lord, he cleanses the hearts of the most fallen people; therefore he extinguishes the blazing fire of the material world. Not only that, he broadcasts the shining brightness of Kṛṣṇa's effulgence throughout the world. Such an ācārya, or spiritual master, should be considered nondifferent from Kṛṣṇa— that is, he should be considered the incarnation of Lord Kṛṣṇa's potency. Such a personality is kṛṣṇāliṅgita-vigraha—that is, he is always embraced by the Supreme Personality of Godhead, Kṛṣṇa. Such a person is above the considerations of the varṇāśrama institution. He is the guru, or spiritual master, for the entire world, a devotee on the topmost platform, the mahā-bhāgavata stage, and a paramahaṁsa-ṭhākura, a spiritual form only fit to be addressed as paramahaṁsa or ṭhākura."
(Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura in his Anubhāṣya quoted in Caitanya-caritāmṛta Madhya 25.9, Purport)