The Bhagavad Gita ('Song of the Lord') is thought to have been written some time between 400 and 100 BC. Technically it is not an individual work - it is a section of the epic Mahabharata - but it is frequently published and discussed as if it was. To this day, it remains the single most influential and popular work of Hindu philosophy ever written, and it is also the first work devoted explicitly and wholly to yoga. Its narrative concerns a moral dilemma faced by Prince Arjuna, who is advised by Lord Krishna as to the best course of action regarding how he should regain his lost kingdom. 

The first and foremost lesson of the Bhagavad Gita is regarding the importance of action - that we have a moral imperative to act, and that by implication non-action is an immoral choice when faced with a dilemma. But this action should always be conducted without selfish motivation. Thus the principle of Karma Yoga, of selfless action. It distinguishes several types of yoga according to what is most appropriate for the different nature of people, such that a devoted person will be most suited to the duty of Bhakti yoga, an intellectual person to Jnana yoga and so on. 

The Bhagavad Gita talks of four branches of yoga: 

(1) Karma yoga (sometimes called Kriya yoga), the yoga of action in the world

" With the body, with the mind, with the intellect, even merely with the senses, the yogins perform action toward self-purification, having abandoned attachment. He who is disciplined in yoga, having abandoned the fruit of action, attains steady peace..." (Ch5:V11-12) 

(2) Jnana yoga, the yoga of knowledge and intellectual endeavor

" When he perceives the various states of being as resting in the One, and from That alone spreading out, then he attains Brahman. They who know, through the eye of knowledge, the distinction between the field and the knower of the field, as well as the liberation of beings from material nature, go to the Supreme." (Ch15:V31/35) 

(3) Bhakti yoga, the yoga of devotion to a deity

".... those who, renouncing all actions in Me, and regarding Me as the Supreme, worship me... of those whose thoughts have entered into Me, I am soon the deliverer from the ocean of death and transmigration, Arjuna. Keep your mind on Me alone, your intellect on Me. Thus you shall dwell in me hereafter." (Ch12:V6-8) " And he who serves me with the yoga of unswerving devotion, transcending these qualities [binary opposites, like good and evil, pain and pleasure] is ready for absorption in Brahman." (Ch14:V26) 

(4) Raja yoga, the yoga of meditation

" Establishing a firm seat for himself in a clean place... having directed his mind to a single object, with his thought and the activity of the senses controlled, he should practice yoga for the purpose of self-realization. Holding the body, head and neck erect, motionless and steady, gazing at the tip of his own nose and not looking in any direction, with quieted mind, banishing fear, established in the brahmacharin vow of celibacy, controlling the mind, with thoughts fixed on Me, he should sit, concentrated, devoted to Me. Thus, continually disciplining himself, the yogin whose mind is subdued goes to nirvana, to supreme peace, to union with Me." (Ch6:V11-15)

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