Object and Objectless Concentration
The four stages  of concentration described in the previous sutra (1.17) were all concentration with object, which is called samprajnata samadhi. In the current sutra,  concentration without any object is being described, and this is called  asamprajnata samadhi. In this state not only the gross and subtle thoughts, but  also the senses and thinking instruments of mind are in a latent state. It is a  very high state of knowing, and is of the kind that is often described as not  describable in words.

When the spiritual aspirant has achieved the highest  degree of concentration upon a single object, he is ready to attempt the  supreme feat – concentration upon consciousness itself. This is the state of  perfect Yoga in which one passes beyond Prakriti, beyond all objective  knowledge, into union with the Atman – the undifferentiated universal  consciousness.
This state of perfect Yoga can only be entered into when  the thought waves have been stilled and the mind has been cleared of all its samskaras,  tendencies, both good and evil, when Mr.Patanjali has ceased to believe that he  is Mr.Patanjali and knows that he is none other than the Atman. Yoga philosophy  is emphatic that it is the samskaras alone that drive us from birth to birth  because our desire to return and plunge into sense experience again and again  is far deeper than we believe. Our temporary reforming tactics like new year  resolutions count for nothing.

It follows that when the samskaras have been rooted out  and destroyed completely (which is the aim of Yoga) there will neither be any  urge towards rebirth nor any necessity for it any longer. He who achieves this  pinnacle of success in Yoga is said to be LIBERATED. He is stated to be with an  awakened mind. All human experiences, sorrow, grief, anxiety, suffering, doubt,  restlessness and pain and what not are left behind. It is like the one having  reached a mountain top, a STATE OF NO MIND or SAMADHI or NIRVANA or MOKSHA.

When you reach the peak, that in which you were caught  and through which you were looking at the top when you were climbing  viz. the towering trees, big creepers and  thorny bushes, now become like a dimensionless green carpet. They no longer  tower above you. They are leveled. You are towering above them and they look  like a mere green carpet as though they have no height at all. So the whole  relationship is changed. The view becomes more spread out. It becomes a  Universal Vision.

This state of intense concentration is achieved by the  spiritual seeker through faith, energy, focus, absorption and knowledge.

What Next?
When a man with such an awakened mind casts away his  mortal body, he will be united with the Atman forever. However, the achievement  of perfect Yoga does not necessarily mean the immediate end of mortal life. Many  saints have reached supreme spiritual experience and continued to live on for  many years. They have continued to think, speak and act on the plane of  external phenomena – but with a difference. The thoughts, words and deeds of a  liberated man are said to be like ‘burnt seeds’ i.e. they are no longer fertile  and fit for germination. So too, samskaras cannot create any new additions or  bondage in a liberated man while he spends his remaining life time which will  be governed by his prarabhdha karma i.e. karmas which were already in  existence before his liberation.

He is like an actor on the last night of a play.  He knows that the play will never be  performed again no matter how well he plays his role, no matter whether the  audience boos or applause. He has nothing to gain or loose by his performance.  Nevertheless, he must play it through to the end till the curtains fall and he  can go home. Speaking of the actions of one who has achieved liberation,  Shankara  tells us “Such actions are  performed as it were, from memory. They are like the remembered actions of a  dream”.

Can we give any example of  such a Divine Personality, the Knower of Brahman, the one who has Become  Brahman himself? Yes! We can! Such an ideal person is none other than the  Jagadguru, Bhagavadpada Adi Shankaracharya.