Previous Folk Religion in India

A-Karma Yoga

"Karma" means literally "action."  It came to be associated particularly with action fulfilling one's social responsibilities, and with the merit one gains by fulfilling one's duties.  Accumulating "good karma" brings a better life when a person is reincarnated.

"Yoga" in the Bhagavad Gita has a broad meaning referring to any religious practice.

B-Bhakti Yoga

"Bhakti" refers to emotionally felt personal devotion to a god or goddess.  It is commonly associated with such things as singing hymns, performing rituals in honor of the god/goddess, and so on.

Karma Yoga refers to performing the duties pertaining to one's social role.  In India, social roles were closely tied to the caste one was born into (Brahmin/priests, Kshatriya/ruler-warriors, Vaishya/farmers-merchants-artisans, Sudras/servants), but this system is not essential to the teaching of the Bhagavad Gita.  Today, karma yoga could be seen as being a good parent, student, policeman, lawyer, etc. The Bhagavad Gita was written by members of a group who had a strong personal devotion to one particular god, Krishna.

 

C-Sankhya Philosophy and Meditation

"Sankhya" means literally something like "analysis."  In the Gita it refers to a particular philosophy associated with a meditation practice.  This is probably not part of traditional folk religion, but a more recent development in India, among people dissatisfied with participating in ordinary social life and traditional religious ritual, seeking for something higher.
Sankhya Philosophy is extremely dualistic, dividing the world into two realms entirely distinct from each other.

1- Atman and Brahaman.  Meditators looking deep into themselves can perceive part of their being called Atman, their "True Self" which is also identical with Brahman, the Supreme Being.  Atman/Brahman is completely free of knee-jerk reactions to things happening in the world.  A person directly experiencing Atman/Brahman also has a feeling of intense spiritual bliss.  Atman/Brahman is beyond change, so a person who identifies with this part of her being enjoys deeply satisfying and undisturbed peace and security.  Everyone has an Atman, but not many people are aware of it.

2-- Prakriti.  Prakriti refers to everything outside of Atman/Brahman.  Prakriti is conceived of a as a great impersonal machine, run by impersonal/mechanical forces called gunas.  Prakriti includes the entire material world, as well as those psychological activities that are unfree reactions to stimuli from the external world (e.g. anger in response to a slap in the face).  Many people identify with these reactions ("I am angry"), but these are people the Gita regards as ignorant of their true self.  They think it is their "self" reacting, when it is only "gunas [of the external world] acting on gunas (of the internal/psychological world).  Involuntary angry responses are not "my" responses, they are "happening to me," and not even happening to the real me (myself as Atman) which is separate from them.

 

Sankhya Philosophy Karma-Yoga and Sankhya

A) How Sankhya philosophy threatens to undermine Karma Yoga, and B) how the Gita's author overcomes this threat, integrating Sankhya philosophy with Karma Yoga.

 Bhakti-Yoga and Sankhya

A) How Sankhya philosophy threatens to undermine Bhakti Yoga, and B) how the Gita's author overcomes this threat, integrating Sankhya philosophy with Bhakti Yoga.
Sankhya Philosophy, carried out consistently in a literal-minded way, threatens to undermine Karma Yoga and Bhakti Yoga A) "Karma" means "action."  A literal-minded understanding of Sankhya would lead to trying to remain "action-less" -- "renouncing karma/action":as the Gita puts it.  But karma also has special  reference to performing social functions, this would also mean refusing to contribute to the functioning of society. A) Atman/Brahman is something completely invisible, "Unmanifest" -- it cannot be represented by normal words or images.  Gods such as Krishna are represented as person-like beings.  Worship of Krishna is directed toward visible representations like pictures and statues.  Literal-minded Sankhya devotees would look down on this worship as a sure sign that the worshippers mistake the visible god Krishna for the highest, unmanifest Supreme Being Brahman.
The author of the Bhagavad Gita is worried about this perceived threat.  He is devoted both to Sankhya philosophy and meditation, and also to Karma Yoga and Bhakti Yoga (for different reasons, I think).  He wants to show how Sankhya philosophy can be integrated with Karma and Bhakti Yoga, combined into a coherent way of life. B) "Perform action (karma) without attachment to the fruits of action, for the maintenance of the world."  A person identified with her Atman does not need to perform any social functions, or be "successful" in the world, as a source of self-esteem.  But she should contribute to society anyhow, out of purely altruistic concern for others.   Performing well socially, without dependence on anything personally gained by such performance, is the ideal advocated in the Gita. B) The Gita admits that there are some "ignorant" people who worship Krishna as the highest god, unaware of the unmanifest Brahman as Supreme Being known to Sankhya philosophers.  But he wants to integrate Krishna-bhakti with Sankhya philosophy, by regarding Krishna as just a manifest representation of the  unmanifest Brahman. A person can show her devotion to Brahman both by meditating and by worshipping at the Krishna-shrine.