The other aim of yoga, in addition to seeing through the false concept of being a separate doer-entity described in my previous post, is to remove compulsive desires. When these have been removed, the result is peace of mind which in turn leads to the ending of suffering and moksha (freedom, liberation).
We could classify desires into two types, compulsive and non-compulsive. Compulsive desires are ones that you feel compelled to enact. Your happiness depends upon fulfilling these desires. Non-compulsive desires are ones which you could take or leave. While you may enjoy the consequences of acting out and fulfilling a non-compulsive desire, your sense of happiness and wellbeing does not depend on it. You could call non-compulsive desires preferences.
When a compulsive desire is not fulfilled, suffering is the result. When a non-compulsive desire is not fulfilled, it’s ok. You may have wanted it to pan out a certain way, but it’s fine that it didn’t happen the way you wanted it to.
When compulsive desires have been rooted out, our happiness no longer depends on objects, and the mind becomes peaceful (sattvic).
In the Bhagavad Gita, Krishna repeatedly advises Arjuna to practice yoga. By this Krishna means to practice not minding what happens regardless of the outcome of a situation. In his first lesson to Arjuna on the subject of yoga, Krishna defines yoga as follows, a definition that is often repeated in various ways throughout the text:
yogasthaḥ kuru karmāṇi saṅgaṃ tyaktvā dhanañjaya
siddhyasiddhyoḥ samo bhūtvā samatvaṃ yoga ucyate
Perform actions, Dhananjaya [Arjuna], giving up attachment, be steadfast in yoga, be equal in success and failure. This evenness of mind is called yoga.
Bhagavad Gita 2.48
So in summary, what is the essence of yoga? Well according to the Bhagavad Gita, yoga essentially means ‘evenness of mind’, or as I put it, not minding what happens. Practice of this leads to having a peaceful (sattvic) mind. All forms of yoga have this sattva and peace as their aim, with the exact methods and mechanisms varying depending on the type of yoga.