Any person that sits down in meditation and tries to stop their thoughts will soon found out that this is practically impossible for long periods of time - perhaps not even for more than a few seconds. Thoughts arise, develop, and fall, without our doing.
The more we observe this experience inside ourselves of thoughts arising, developing, and falling away without our doing, the more it becomes clear that we are not creating these thoughts.
Similarly to how the heart pumps blood, the mind produces imaginations, memories, and inner dialogue, without our doing. This gives rise to interesting questions:
Where do these thoughts come from
Who/what is creating these thoughts?
And why are my thoughts different than someone else’s? Yoga philosophy can give us an answer to this question by describing different layers to our human being, from the most physical to the most subtle.
The gross body. Not gross as un yuk ;-), but as in the most dense/physical layer of our existence; our physicality.
The subtle body. The subtle realm of mind, ego, thinking, sensing, and energy through which we enjoy and perceive life.
The causal body. Also known as the body of knowledge. It is the - unconscious - storehouse of all our mental imprints, that veals the soul/atma/reality/consciousness.
The answer to our questions is found by understanding the causal body.
The causal body is like an unconscious storehouse of a lifetime of experiences and habits, from which thoughts and tendencies (also known as vasana’s) are being brought into the mind-space. These vasana’s can be both pure or impure; helpful or destructive.
The quality of our causal body and vasana’s will determines the quality of our lives; the quality of our thoughts and habits, the natural triggers and responses we have to circumstances, and the quality of our subtle beliefs and emotions.
Any good spiritual practice is in some way or another oriented towards lessening the bondage to the causal body and to purify it gradually, so we can align and establish ourselves with truth and happiness.
To cut the bondage it is most important that we:
1. Have insight into our true nature, by discerning very clearly between what is truly ours (conscious perception) and what is pretending to be ours (thought-forms, identity, shadows, etc).
2. Live our lives according to this insight into our true nature.
By maintaining wakefulness and remembrance of our true nature in our day to day life, we will naturally recognize and burn away the impurities that arise in our day to day experience.
Quite literally, the truth will set you free.