SB 11.3.29 — One who desires his ultimate self-interest should cultivate friendship with those persons who have accepted Kṛṣṇa as the Lord of their life. One should further develop an attitude of service toward all living beings. One should especially try to help those in the human form of life and, among them, especially those who accept the principles of religious behaviour. Among religious persons, one should especially render service to the pure devotees of the Supreme Personality of Godhead.