SB 11.3.29
evam krsnatma-nathesu
manusyesu ca sauhrdam
paricaryam cobhayatra
mahatsu nrsu sadhusu
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
One who desires his ultimate self-interest should cultivate friendship with those persons who have accepted Krsna 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 behavior. Among religious persons, one should especially render service to the pure devotees of the Supreme Personality of Godhead.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
According to Srila Bhaktisiddhanta Sarasvati Thakura, the highest duty for devotees of the Supreme Lord is to establish friendship with those who have completely surrendered to Krsna and who have thus achieved saranagati, shelter at the Lord’s lotus feet. One should render service to both the Lord and His devotees, since the Lord is more pleased by sincere service rendered to His pure devotees. One should not only officially offer respect to the Supreme Personality of Godhead, His devotees and His worshipful paraphernalia, but should actually render service to the representatives of the Lord, who are known as maha-bhagavatas.