The Only Definition of Bhakti
Sri Hari Bhakti Kalpa Latikā
The definition of bhakti is devotional service rendered to Lord Krishna with no expectation of remuneration or other self-centred interest. Such pure devotional service is said to bring the Lord under the control of His devotees. It is the mutual love between the Lord and His devotees that is the cause of bringing Him under their control. The true wealth of a devotee is hidden to those who are ignorant of this confidential fact. A devotee whose only wealth is Krishna is usually scorned by materialists who think of him as a social misfit. However, a devotee is fully satisfied, completely peaceful at heart, and he possesses a valuable asset that can¬not be taken away, even at the time of his death. All the mystic perfections, the hosts of demigods, and even Laksmi devi, are forever waiting to serve a devotee of Krishna. However, a devotee has no aspiration other than the loving service of Krishna.
— Sri Hari Bhakti Kalpa Latikā – Author Unknown,Unsigned Manuscript; Published by His Divine Grace Bhaktisiddhanta Sarasvati Thakura Prabhupada