The word ‘Yoga’ literally means ‘union’, i.e., spiritual union of the individual soul (Jivatma) with the Universal Soul (Parmatma). Sage Patanjali, the author of “Yoga Sutra” begins his Yoga Sutras with the definition of yoga as “restraining the mind-stuff (Chitta) from taking various forms (Vrttis)” i.e. Chitta vritti nirodha (1:2). Swami Vivekananda in his commentary on Yoga Sutra compares Chitta to the lake where the waves are the Vrttis. As soon as the waves have stopped, and the lake has become quiet, we see the ground below the lake. So with the mind; when it is calm, we see what our own true nature is.

To achieve this purpose of restraining the Chitta, Yoga gives us the Eightfold Path of Discipline or the “Ashtanga Yoga”. The prescribed eight sadhanas to control “Chitta” are the following; 1. Yama, 2.Niyama, 3.Asana, 4.Pranayama, 5.Pratyahara, 6.Dharana, 7.Dhyana, 8. Samadhi. 

The Yoga-sutra of Patanjali contains 196 aphorisms or Sutras arranged in four parts. The first part is called samadhi-pada which deals with the nature and aim of concentration. The second, sadhana pada, explains the means to realize this end. The third, vibhutipada, deals with the supernatural powers (Siddhis) which can be acquired through Yoga. The fourth, kaivalyapada, describes the nature of liberation and the reality of the transcendental self. 

Patanjali Yoga Philosophy is based upon Samkhya Philosophy, the only difference being that there is no place for God in the latter. The Yoga, therefore, is described as the Samkhya with God. “Iswara” (God) is one of the many objects on which Yogis can concentrate their mind. Patanjali defines God as a special kind of Purusha who is always free from pains, actions, effects, and impressions. He is eternally free and was never bound nor has any possibility of being bound. He is above the law of karma. He is omniscient, omnipotent and omnipresent. He is perfection incarnate. He is the purest knowledge. Yoga Sutra also specifically mentions that Aum (Om) is the symbol of Ishvara.

The Sutras dealing specifically with Ishwara are listed below with English Translations:

ईश्वयप्रणिधानाद वा ॥ 1.23॥

Or by devotion to Isvara(that state can be achieved).

क्लेशकर्मविपाकाशयैरपरामृष्टः पुरुषविशेष ईश्वरःll1.24॥

Isvara (Supreme Ruler) is special Purusa, untouched by misery, results of actions, or desires.

तत्र निरतिशयं सर्वज्ञबीजम् (1.25)

In God, the seed of omniscience is at unsurpassable level. 

स पूर्वेषाम् अपि गुरुः कालेनानवच्छेदातस पूर्वेषाम् अपि गुरुः कालेनानवच्छेदात् (1.26)

Not being limited by time, He is even the master of the ancients.

तस्य वाचक् प्रिव् (1.27)

His manifesting word is Om.

समाधिसिद्धिरीश्वरप्रणिधानात् (2.45)

By sacrificing all to Isvara comes Samadhi. By resignation to the Lord, Samadhi becomes perfect.