Bhagavad Gita Verse 55, Chapter 18

bhaktyaa maamabhijaanaati yaavaanyashchaasmi tattvataha |
tato maam tattvato jnyaatvaa vishate tadanantaram || 55 ||
 
Through devotion he knows me in essence, what I am and who I am. Then, having known me in essence, he enters into me immediately.
 
bhaktyaa : through devotion
maam : me
abhijaanaati : knows
yaavaan : what I am
yaha : who
cha : and
asmi : I am
tattvataha : in essence
tataha : then
maam : me
tattvataha : in essence
jnyaatvaa : known
vishate : enters into me
tadanantaram : immediately
 
Shri Krishna describes the final stage, the ultimate goal, of the sanyaasi in the shloka. So far, the monk only had a conceptual understanding of Ishvara's true nature. But, when his devotion to Ishvara reached its peak, when his individuality has been destroyed, when he sees Ishvara as his own self and not someone standing outside of him, he understand what Ishvara is in his essence. When that happens, his identity merges with Ishvara’s identity. He enters, he merges into Ishvara. Knowing Ishvara in essence and merging into Ishvara are the same.
 
So then, this is true jnyaana, true knowledge. Shri Shankaraachaarya describes this pure understanding of Ishvara as one without a second, absolute, awareness, birthless, ageless, immortal, fearless and deathless. This is the meaning of the word yaha, meaning who I am, in the shloka. The word yaavaan, what I am, refers to the differences in Ishvara creates by his upaadhis, by his maaya. The ability to arrive at this distinction is the culmination of the seeker’s efforts towards chitta shuddi, towards purifying his mind.
 
Now, what is the connection here between devotion and knowledge, between bhakti and jnyaana? It is said that jnyaana is the fruit of bhakti. When bhakti ripes, jnyaana arises. Bhakti cleanses the mind of all its impurities, and consequently, removes the sense of separation or individuality between the seeker and the world. The seeker, having understood that his self and Ishvara's self are one and the same, having understood the "asi" in "tat tvam asi", "you are that", he merges into Ishvara. The highest teaching of the Gita has been concluded with this shloka.