In letters on yoga Sri Aurobindo said theres the vital which brings us outward and downward and theres the psychic which is aways close to Mother. Then there is the witness purusha which has to choose where it sides and has to stand with the psychic and reject the lower movements. What is the difference between the witness purusha and the soul, are they the same thing? How does one make the witness purusha stand on the side of the psychic🤨?

The Witness Purusha is the inner being, mainly the inner mental that can separate itself and stand back from the workings of outer nature. This mental being that is capable of separating itself and watching the lower movements should not be just a passive Witness but a dynamic mental will giving or denying sanction to the vital movements. This it can do only if it is awakened to wisdom by the light of the psychic that is still deeper within. Basically this mental will should be turned towards the Divine in an aspiration for the Divine. Then it begins to grow intuitively aware of what is to be accepted and what is to be rejected. 

Affectionately,

Alok Da