Bhagavad Gita Verse 25, Chapter 5

labhante brahmanirvaanamrishayaha ksheenakalmashaaha |
chhinnadvaidhaa yataatmaanaha sarvabhootahite rataaha || 25 ||
 
The wise seeker, whose defects have been destroyed, who has eliminated all doubts, who has complete control over his self, who is engaged in the welfare of all beings; he obtains liberation.
 
labhante : obtains
brahmanirvaanam : ultimate liberation
rishayaha : that wise seeker
ksheena : have been destroyed
kalmashaaha : all defects
chhinnadvaidhaa : all doubts have been eliminated
yataatmaanaha : who has complete control over his self
sarvabhoota : all beings
hite : welfare
rataaha : engaged
 
In this shloka, Shri Krishna further explains the nature of one who is liberated by establishing himself in the eternal essence. Such a liberated seeker is called a "rishi". It means one who knows, one who has knowledge of the eternal essence. Typically, we think of a rishi as someone who has a beard and wears a robe. It is not so. A rishi uses knowledge and discrimination constantly and knows the difference between the real and the unreal. Such a rishi has four attributes per this shloka: free of all defects, free from all doubts, complete self control, and engaged in the welfare of all beings.
 
The rishi is "ksheena-kalmasha", which means that he has freed himself of all mental impurities. The core or the key mental impurity is ignorance which manifests in the form of affinity for worldly pleasures. It is ignorance alone from which all impurities are others based off. It is through karmayoga that we rid ourselves of all mental impurities.
 
Next, the rishi is "chhinna-dvaidah". He is free from all doubts regarding who is really is. Until the mind has doubts, the notion that "I am the eternal essence" will come and go, but it will not be permanent. There will be no conviction behind it. Desires that push us out into the world are the obstruction to such a permanent conviction. "Chhinna - dvaidah" also means free of all notions of duality.
 
"Yataatmaanah" is another word used to describe the rishi. He has complete self control, in other words, he has compete control over his mind and senses. He is not like most of us who are under the mind's control. The rishi know that the body, mind and senses are different than his true self which is the eternal essence. Once he realizes that they are different than him and have no relation to him, he does not come under their control.
 
Furthermore, the rishi is "sarva bhuta hite rathaah", which means that he is always engaged in the welfare of all. Now this does not mean necessarily that he is engaged in social service. It means that the rishi is always in a state of total non-violence. He sees no distinction between himself, one person and another person.It is like water and the fish. Regardless of what the fish does, the water lives in total harmony with the fish. One has no fear for the other.
 
So therefore, such a rishi is the one who is fit to attain liberation, where he dissolves himself into the eternal essence, just like a wave dissolves into the ocean.