SB 10.8.4
mahad-vicalanam nrnam
grhinam dina-cetasam
nihsreyasaya bhagavan
kalpate nanyatha kvacit
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O my lord, O great devotee, persons like you move from one place to another not for their own interests but for the sake of poor-hearted grhasthas [householders]. Otherwise they have no interest in going from one place to another.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As factually stated by Nanda Maharaja, Garga Muni, being a devotee, had no needs. Similarly, when Krsna comes He has no needs, for He is purna, atmarama. Nonetheless, He descends to this material world to protect the devotees and vanquish miscreants (paritranaya sadhunam vinasaya ca duskrtam). This is the mission of the Supreme Personality of Godhead, and devotees also have the same mission. One who executes this mission of para-upakara, performing welfare activities for people in general, is recognized by Krsna, the Supreme Personality of Godhead, as being very, very dear to Him (na ca tasman manusyesu kascin me priya-krttamah). Similarly, Caitanya Mahaprabhu has advised this para-upakara, and He has especially advised the inhabitants of India:
bharata-bhumite haila manusya-janma yara
janma sarthaka kari’ kara para-upakara
“One who has taken his birth as a human being in the land of India [Bharata-varsa] should make his life successful and work for the benefit of all other people.” (Cc. Adi 9.41) On the whole, the duty of a pure Vaisnava devotee is to act for the welfare of others.
Nanda Maharaja could understand that Garga Muni had come for this purpose and that his own duty now was to act according to Garga Muni’s advice. Thus he said, “Please tell me what is my duty.” This should be the attitude of everyone, especially the householder. The varnasrama society is organized into eight divisions: brahmana, ksatriya, vaisya, sudra, brahmacarya, grhastha, vanaprastha and sannyasa. Nanda Maharaja represented himself as grhinam, a householder. A brahmacari factually has no needs, but grhis, householders, are engaged in sense gratification. As stated in Bhagavad-gita (2.44), bhogaisvarya-prasaktanam tayapahrta-cetasam. Everyone has come to this material world for sense gratification, and the position of those who are too attached to sense gratification and who therefore accept the grhastha-asrama is very precarious. Since everyone in this material world is searching for sense gratification, grhasthas are required to be trained as mahat, great mahatmas. Therefore Nanda Maharaja specifically used the word mahad-vicalanam. Garga Muni had no interest to serve by going to Nanda Maharaja, but Nanda Maharaja, as a grhastha, was always perfectly ready to receive instructions from a mahatma to gain the real benefit in life. Thus he was ready to execute Garga Muni’s order.