In the Bhagavad-Gita, four grades of bhaktas are mentioned: he who is in distress (arta), he who desires wealth (artharthi), he who seeks knowledge (jijnasu), and he who has gained knowledge (jnani). Of these, declares the Lord, the last excels the others, because he is devoted to the one (eka-bhaktih); in other words, he does not see anyone or anything else to be devoted to.19
The jnani is, verily, the Lord Himself. For the other three grades of devotees, there is the notion of distinction; but in the experience of the Jnani there is not the least difference. The jnaniís mind has become still, and he knows "I am God" - not the ego - 'I'', but the ego-less 'I'. 20
It is by the fourth type of bhakti which is the path of knowledge (jnananistha) that one realizes God truly. It is called supreme because it is above the other three. It is only after the supreme devotion has been gained that the notion of difference as between God and the soul completely disappears.21
19. Sankara's commentary on vii, 17: anyasya bhajaniyasya adarsanat atah sa ekabhaktih visisyate visesam adhikyam apadyate atiricyate ity arthah.
20. Sankara on vii, 18: aham eva Bhagavan vasudevo na anyah asmi iti evam yuktatma samahita-cittah San mam eva param brahma gantavyam anuttamam gatim gantum pravitta ity arthah.
21. Sankara on Gita, xviii, 55: sa iyam Jnana-nistha artadi-bhaktitrayapeksaya para caturthi bhaktih iti ukta. taya paraya bhaktya bhagavantam tattvatah abhijanati, yadanantaram eva isvara-ksetrajna-bhedabuddhih asesato nivartate.