Who is a pure devotee?

According to Śrīla Śrīdhara Svāmī, the essence of a pure devotee’s qualifications is one who has attracted the Lord by his love so that the Lord cannot give up the devotee’s heart. According to Śrīla Jīva Gosvāmī, the word sākṣāt in this verse indicates that a pure devotee has realized knowledge of the Supreme Personality of Godhead, having given his heart to the Supreme Lord, Kṛṣṇa, who is all-attractive in six opulences, including beauty. A pure devotee can never be attracted by the fleshy bags of women’s breasts or by the hallucinations of so-called society, friendship and love within the material world. Therefore his clean heart becomes a suitable abode for the Supreme Lord. A gentleman will live only in a clean place. He will not live in a polluted, contaminated place. Educated people in the Western countries are now greatly protesting the pollution of water and air by urban industrial enterprises. People are demanding the right to live in a clean place. Similarly, Lord Kṛṣṇa is the supreme gentleman, and therefore He will not live in a polluted heart, nor will He appear within the polluted mind of a conditioned soul. When a devotee surrenders to Lord Kṛṣṇa and becomes a lover of the Lord by direct realization of Kṛṣṇa’s all-attractive nature, the Lord makes His residence in the clean heart and mind of such a pure devotee.

Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Eleventh Canto, Chapter 02 – Text 55.