In Bhakti there are four letters. It's made up of "bha", "ka", "ta", and "i" (ee). "Bha" stands for fulfillment and nourishment. "Ka" stands for knowing - a means of knowing. "Ta" stands for redeeming, for saving, for salvation. "I" (ee) stands for shakti.
So in Bhakti four things are there: fulfillment and nourishment; means of knowing; "tarana" or salvation; and energy. Bhakti saves you. Bhakti nourishes you. Bhakti is the means of knowing, the right knowledge. When Bhakti is there the doubts don't come. It gives the most energy. So Bhakti contains as the seed all the four qualities.
All the emotional upheavals one undergoes is because one doesn't know Bhakti. When all intense feelings flow in one direction that is Bhakti, it becomes Bhakti. What is the difference between a canal and a flooded field? In a flood what happens is the water does not have a bank to flow in. When the water flows within banks you call it "river". When water is scattered all over, it's all flooded. So when the emotions get flooded everywhere, mind is in a mess. If it is intensely flowing in a direction, then that is Bhakti. And that is most powerful.
A sign of Intelligence is Surrender or Bhakti.