Bhakti comes from the word bhaj-dhatu, so this word has been used, bhajate mam; it means "engaged in devotional service." Yoginam api sarvesam mad-gatenantaratmana — "a person who is keeping Me always within the core of the heart."

The best example are the gopis. They had no other business than to keep Krsna always within the heart. Gopis requested Krsna, "Please, if You get out from our hearts then we can concentrate to our household duties. These yogis and munis and great saintly persons, they are trying to keep You within the heart, and we request You, 'Kindly go out of our hearts so we can concentrate on our household duties.' " They wanted to do it, but they could not. This is gopis' position.

Therefore Caitanya Mahaprabhu has advised, ramya kacid upasana vraja-vadhu-vargena ya kalpita: there is no more better method of worship than what was done by the gopis, because gopis always kept Krsna within their hearts. So therefore they are the most perfect yogis.

(Srila Prabhupada, lecture — February 7, 1974)