Here is the answer. After all the negations — not by Vedas, not by penance, not by charity, not by sacrifice — Krishna names the one thing that works: ananya bhakti. Undivided devotion. Not devotion mixed with ambition. Not devotion as a strategy. Devotion that has nowhere else to go.
And Krishna describes three stages of what this devotion makes possible. First, jnatum — to know Him. Second, drashtum tattvena — to see Him in truth, as He really is. Third, praveshtum — to enter into Him. Knowing is intellectual understanding. Seeing is direct experience. Entering is union. The progression moves from the head to the heart to complete dissolution of the boundary between devotee and divine.
The word 'ananya' is the key. It means 'not directed toward another.' A river that flows toward the ocean does not stop to fill every pond along the way. It moves, steadily, toward one destination. That is ananya bhakti — devotion with a single direction, a single focus, a single home.