What is Bhakti? -Bhagavan Shankara

There is a little difference in opinion between the teachers of knowledge and those of love, though both admit the power of Bhakti. The Jnanis hold Bhakti to be an instrument of liberation; the Bhaktas (devotees) look upon it both as the instrument and the thing to be attained.

To my mind this is a distinction without much difference. In fact, Bhakti, when used as an instrument, really means a lower form of worship and the higher form becomes inseparable from the lower form of realization at a later stage.
Each seems to lay a great stress upon his own peculiar method of worship, forgetting that with perfect love true knowledge is bound to come even unsought, and that from perfect knowledge true love is inseparable.

Bearing this in mind, let us try to understand what the great Vedantic commentators have to say on the subject.,Bhagavan Shankara says, “Thus people say, ‘He is devoted to the king, he is devoted to the Guru’; they say this of him who follows his Guru, and does so, having that following as the one end in view. Similarly they say, ‘The loving wife meditates on her loving husband’; here also a kind of eager and, continuous remembrance is meant.” This is devotion according to Shankara