Samkhya-Yoga-Kundalini
The philosophy of yoga is explained in a nutshell by these three sutras:
1.2 - Yoga is the restraint of the activities of consciousness.
1.3 - Then the seer [i.e. the Self] abides in its own form.
1.4 - At other times there is conformity [of the self] with the fluctuations.- adapted from the translation by Georg Feuerstein
This gives us the big picture. Let’s examine these one by one, in reverse order.
Vṛtti-sārūpyam-itaratra
At other times (itaratra) there is conformity (sārūpyam) [of the self with] the activities. (Vṛtti).
This is where we are now, the usual condition of human consciousness. As we go about our daily lives, we falsely identify with the activity of our minds.
Tadā draṣṭuḥ svarūpe’vasthānam
Then (tadā), the Seer (draṣṭuḥ) abides in (avasthānam) its own-form (sva-rūpa).
This is where we want to go. The self no longer falsely identifies with the activities of the mind. It now correctly understands its true nature.
Yogaś-citta-vṛtti-nirodhaḥ
Yoga is the restraint (nirodhaḥ) of the activities (vṛtti) of consciousness (citta).
This is how we get there. Let’s look at each word individually.
Yoga is the subject of the definition. It is one of many words that Patanjali defines for us.
Usually translated as “the mind” or “consciousness”. Citta is defined precisely by its vrtti.
Vrtti is variously translated as fluctuations, modifications, or functions, among other things. Patanjali enumerates five citta-vrtti:
Citta cannot be perceived directly. Its existence is inferred from the common experience of the vrtti.
Nirodha is variously translated as restraint, restriction, focusing, or stopping. There seems to be a bit of conflict, since stopping or cessation is different from restraining or focusing. In reality, nirodha is both the act of focusing or restraining and the end result of doing so, which is complete cessation of citta-vrtti. Only the most advanced yogis get to the point of complete cessation. Students should not attempt to sit in meditation and stop their mind. The Eight Limbs contains methods that help the yogi to calm and focus the citta-vrtti.
Vṛttayaḥ pañcatayyaḥ kliṣṭā akliṣṭāḥ
The five citta-vrtti may be afflicted or not afflicted.
This is a very important point. Those who minds are disturbed by delusion, anger, greed, or passion in general need to correct those things before yoga is possible. A large part of the Yoga Sutras is concerned with overcoming those sorts of things.