Yoga Sutra is brief presentation on yoga (meditation) which is means for moksha (liberation from the sense of limitation / liberation from the life of becoming).
Even though for Yoga, by practice asamprājnata samadhi alone for secession of the mind, one will get moksha. But for us (vedantin) by cognitive separation itself, understanding I am the only reality through sravanam (learning the scripture with guidance of teacher), mananam (resolving the doubt), and nididhyasanam (removing the habitual error), one abides in one's own true nature.
Yoga sutra contains of 4 पाद sections, with total 195 sutras are there:
1st section called samadhīpada, deal with meditation (51 Sutras) 2nd section called sādhanapada, deal with means for meditation (55 sutras)
3rd section called vibhūtipada, deal with extraordinary power (55 sutras)
4th section called kaivalyapada, deal with state of being just oneself (34 Sutra)
1-1 atha yogānuśāsanam
Thereafter, begin the teaching in keeping with yoga (meditation) tradition.
The word अथ atha, utility wise use for auspiciousness when the author starting any text, because grace is needed for the text to be completed, and also the text should reach the right audience. Here also implies the qualification of the students who received the teaching. The qualifications at patanjali time should have a big gap compare to now, but at least we are who sitting here value the meditation itself.
1-2 yogascittavrttinirodhah Constrain / mastery over the modification of the mind.
Modification of the mind is a important keyword here. Because only by knowing how the mind's tendencies are, then we know how to handle it well.
5 state of mind are there:
Ksiptam, wondering / scattered, mind busy with sense object.
Mūdham, dull state, sluggishness.
Viksiptam, mind got focus but often distracted.
Dekagram, focus on object of meditation without getting distractions, also call samprajnāta samadhī
Asamprajnāta samadhī, resolution of thought, there is no subject-object division between meditator and object of meditation.
The word Yoga in this text, means the last two state, with the culmination on the last state asamprajnāta samadhī.
Question: Now what is happened after highest culmination?
1-3 tadā drastuh svarupevasthānam Then (at time of resolution of all though in asamprajnāta samadhī), the person (Atma) remaining in his true nature (moksha).
Question: If samadhi is not there, what is the situation of this Atma?
1-4 vrttisārūpyamitaratra
At other time (when samadhi is not there), there is identification (of Atma) with thoughts.
Sarūpyam means whatever the form of the thought, Atma assume the form of that though. In sastra the example of the crystal appear red when red flower is there in proximity. The self superimposed to non self. Assumed the though is not like that you think about your love one the you will become him or her. The thought will bring feeling of happiness or sadness, then Atma will identify with that feeling and become it as it were. I am happy person, I am an unlucky person.
The approached of yoga is to remove the red flower then crystal will be in its true color. But vedanta approach is as long as you are cognitively remove the red flower, Atma is completely free from all the problem we though we were.