According to Swami Vivekananda, "Bhakti without Vedanta is superstition and Vedanta without Bhakti is madness!". So what is this Bhakti without which the pursuit of Vedanta becomes madness?
True Bhakti is just surrendering with all your heart.
It’s probably easier to comprehend this in the context of thoughts and actions aimed within Maya. For such goals, we all know it is difficult to succeed unless your mind as well as heart is set on the goal. Of course, pursuing the goals of the lower nature that are trapped within Maya makes your mind more agitated and excited rather than calm and serene. But nevertheless once your heart is in it you have a higher probability of success.
The exact same principle applies to the higher goals as well. However, for higher goals where the goal itself is difficult to envision using our senses, where contemplation is the tool and selfless actions is the path, the question then becomes surrender to what? Which is probably where worship of the Ishwara (Gods that your mind can imagine or the imaginary-Gods) help as they, being manifestations within Maya, are more comprehendible yet being a common or shared entity (not an individual property like my-wife, my-child, my-self, my-...) reduce the "I-ness" in the pursuit of the ultimate jnana.
Surrendering with all your heart to that which you cannot comprehend, where your intellect alone cannot reach, where science ends and philosophy starts is true Bhakti. And unless you truly surrender, intellectual contemplation (jnana yoga) or selfless actions (karma yoga) will not be effective.
Whatever is easy for you to surrender to - an Iswara or a person who in your mind is of a higher nature or the incredible play of nature or the higher goal in its very abstract form - is a personal choice as long as the goal is the true understanding or self-realization. This Bhakti will help you reach your higher goal using contemplation (thought experiments, extrapolation and self-inquiry) and selfless actions.