Bhagavad-gita (by Krishna), Srimad Bhagavatam (about Krishna)

Verse 1.1.23: Basically Bhagavad-gita is the narration of Krishna himself, and Srimad Bhagavatam is a narration of devotees about Krishna. In Bhagavad-gita, Krishna does not talk about Himself, but what we are supposed to do to achieve the perfection of life. He explains sankhya yoga, gyana yoga, astanga yoga and finally bhakti yoga and also tells that the highest and the most sublimes process is Bhakti yoga. Krishna explains in the Bhagavad-gita, how living entity falls down, how we can cleanse our heart and reunite with Krishna in the spiritual world. So Krishna is giving the process here without telling anything about Himself.

Whereas, in Srimad Bhagavatam, it is given how devotees apply the principles given in Bhagavad-gita and go back home back to Godhead. The culmination of that love attained is explained in the 10th Canto, the gopi's. So even ladies, vyasya's and sudra's, it is shown here that even they can become pure devotees. Another example is Narada muni. It is shown that Bhakti is not dependent on birth. Anyone can become a pure devotee by simply chanting Krishna's Holy Name, serving devotees and purifying their existence.

Ending of First Canto, First Chapter.