In other words, the cleansing of the polluted heart by other methods (like the culture of empiric knowledge or mystic gymnastics) can simply cleanse one's own heart, but devotional service to the Lord is so powerful that it can cleanse the hearts of the people in general, by the devotional service of the pure, empowered devotee. A true representative of the Lord like Nārada, Śukadeva Gosvāmī, Lord Caitanya, the six Gosvāmīs and later Śrīla Bhaktivinoda Ṭhākura and Śrīmad Bhaktisiddhānta Sarasvatī Ṭhākura, etc., can deliver all people by their empowered devotional service.
By sincere efforts to hear Śrīmad-Bhāgavatam one realizes his constitutional relationship with the Lord in the transcendental humor of servitude, friendship, paternal affection or conjugal love, and by such self-realization one becomes situated at once in the transcendental loving service of the Lord. Not only were all the pure devotees like Nārada self-realized souls, but they were engaged in preaching work automatically by spiritual impetus, and thus they delivered many poor souls entangled in the material modes. They became so powerful because they sincerely followed the Bhāgavatam principles by regular hearing and worshiping. By such actions the accumulated material lusts, etc., become cleansed by the personal endeavor of the Lord within the heart. The Lord is always within the heart of the living being, but He becomes manifested by one's devotional service.
Purification of the heart by culture of knowledge or mystic yoga may be all right for the time being for an individual person, but it is like the cleansing of a small quantity of stagnant water by chemical processes. Such clarification of water may stand for the time being and the sediments settle down, but by a slight agitation everything becomes muddy. The idea is that devotional service to the Lord is the only method of cleansing the heart for good. Whereas other methods may be superficially good for the time being, there is a risk of becoming muddy again due to agitation of the mind. Devotional service to the Lord, with specific attention for hearing Śrīmad-Bhāgavatam regularly and always, is the best recommended method for liberation from the clutches of illusion.