Bhakti-Shakti: The Power Of Devotion

In his Amrta-pravaha-bhasya, Srila Bhaktivinoda Thakura explains that this spiritual potency is the essence of the pleasure potency and the eternity potency. By these two potencies, one is empowered with devotional service. Lord Krishna Himself, or His representative, the unalloyed devotee, can mercifully bestow these combined potencies upon any man. Being thus endowed with such potencies, one can become an unalloyed devotee of the Lord. Anyone favored by Sri Caitanya Mahaprabhu was empowered with this bhakti-shakti. Thus the Lord's followers were able to preach Krishna consciousness effectively by divine grace.

Purport by A.C. Bhaktivedanta Swami Prabhupada. Caitanya-Caritamrita, Madhya Lila Ch. 7, verse 99