How to make mind free?

What you perceive as suggestions or voices, are accepted and felt by people to be thoughts of their own mind. When one practises Yoga and observes the thoughts, one sees that they come from outside, from universal Nature, from the mental, vital or subtle physical worlds etc. The proper thing is then to stand back from these thoughts, voices or suggestions, to reject them or else control them, to make the mind free and quiet and open only to the divine light, force, knowledge and the presence of the Divine. Your mistake has been to allow free play to these thoughts, voices and suggestions instead of rejecting, silencing and controlling them. It is what you must now do. Aspire, get into contact with the Light and the true Force, reassert your will to reject these suggestions and voices. Do not take interest in these voices, keep the mind quiet.

Ref : Letters on Yoga Vol. IV