There are so many things that we understand, but maybe our feelings and emotions don't match our understanding. Often our understandings go run far ahead of our emotions. The desires suck us out into the world which embroil us in the ups and downs of the world. In the path of knowledge, devotion harnesses all the desires and channels them towards god - saguna brahman.
As part of retreat inspired by the Ashtavakra Gita, Swami Sarvapriyananda speaks on the connection between the path of knowledge and devotion.