Fifteen Steps to  Attain Knowledge
Sankara now expounds the fifteen steps with the help of which on should practice profound meditation at all times on Brahman for the attainment of the desired goal. These are enumerated below.
1.Control of the senses (yama)
2.Control of the mind (niyama)
3.Renunciation (tyaga)
4.Silence (mouna)
5.Space (desa)
6.Time (kala)
7.Posture (asana)
8.Restraining the root (mulabandha)
9.Holding the body steady (deha-samya)
10.Steadiness of gaze (drk sthiti)
11.Control of prana  (prana-samyamana)
12.Withdrawal of the mind (pratyahara)
13.Continuous reflection (dharana)
14.Contemplation on the Self (dhyanam) and
15.Total absorption (samadhi)

These terms have been given special meanings by Sankara,  although some of them were dealt with in the Patanjali Yoga sutras also. The  aspiring one who practices these fifteen sadhanas gets the natural bliss (ananda). The ordinary bliss is ‘kritrima’, a created one, the  creation of the mind through the sense organs. Uncreated or natural bliss is our  nature. Then such a person, the master of all the Yogis, becomes perfect, without  the necessity of any further practices. The nature of such a person cannot be  an object either for the mind or for the speech for the Mundaka Upanishad  (III.II.9) says “He who realizes the Supreme Brahman verily becomes Brahman.”  His nature also merges in that of Brahman which is beyond the mind and speech.  (Taittiriya Upanishad II.9)
Obstacles to Meditation
When a seeker starts his sadhana for Samadhi there will inevitably be some obstructions. These are spelled out as under:
1.Absence of constant spirit of enquiry
2.Idleness
3.Attraction for sensual pleasures
4.Sleep
5.Dullness
6.Distraction
7.Experiencing joy resulting out of concentration
8.Sense of blankness arising out of a conflict of desires.

Constant Thought  of Brahman neccesary
While thinking of any object the mind will entirely identify itself with that alone and while thinking of a void it really becomes blank. But with the thought of Brahman, it attains to perfection. Hence one  should constantly meditate on Brahman to attain perfection. This is based on  the principle ‘as you think so you become.’ One desiring perfection should  leave aside all thoughts of duality and fix one’s mind upon the non-dual  Brahman which alone is perfect.

Man has the unique opportunity of realizing Brahman and  thus becoming free from the bondage of ignorance. But if he does not avail  himself of this rare opportunity, he can be hardly called as a human being as  there remains nothing to distinguish him from the lower births like animals or  insects. Those fortunate few who at every moment feel their identity with  Brahman become completely free from the shackles of duality and ignorance. This  is the consummation of spiritual practice. It is needless to say that they are  respected everywhere and by everybody.

Sankara boldly declares that those only in whom this  consciousness of Brahman ever remains are mature and certainly not others who  merely engage themselves in fruitless arguments and discussions about Brahman  by variously interpreting the scriptures. He continues that those persons who  are only clever in discussing about Brahman but have no realization and are  very much attached to worldly pleasures are born and die again and again as a  consequence of their ignorance. This exposition, called Raja Yoga, ends here.