Bhakti is a means and an end in itself. It's like consciousness rediscovering itself and burning like a untamed flame after having been into oblivion of illusory Maya. Bhakti is one of the paths which lead to self-realization. Gyana, Karma and Bhakti are three types of Yogas. Yoga is the art and science of attaining self-realization or losing false ego or dissolving soul to supersoul or Science to know this universe and various other universes expressed in Hindu Vedas, Puranas and Upanishadas.
Bhakti is, like knowledge, its own prize. It's not that you have to become a devotee to get something or to fulfil a desire; if you get the touch of divine ultimate, every desire of yours would become irrelevant. Those who are self-realized, when they get the to realize their self by Bhakti, don't ask for any favors, but for more Bhakti. The Bhakti, Gyana and Karma appear to be three different paths, but they're one and same. The unperturbed remembrance is key of devotion and so is the essence of Gyana and Karma yogas.
In Gyana Yoga you have to reinforce witness consciousness in meditation by consistent attention. Your mind dissolves into the witness and then witness also dissolves and self shows itself in its full bloomed glory. In case of Karma Yoga, you witness the 'doer,' never assuming yourself as a cause or vital factor in any of your deeds and offer all the Karmas to God. In Bhakti, you remember God by chanting his name, thinking about his image and his deeds, his manifestation and love him like your son, father, mother, friend and neighbor. You see only God in every being and every thing around you.