We must now deal with the mental body, which is taken as equivalent to mind for practical purposes. The first thing for a man to do in practical Yoga is to separate himself from the mental body, to draw away from that into the sheath next above it. And here remember what I said previously, that in Yoga the Self is always the consciousness plus the vehicle from which the consciousness is unable to separate itself.
All that is above the body you cannot leave is the Self for practical purposes, and your first attempt must be to draw away from your mental body. Under these conditions, Manas must be identified with the Self, and the spiritual Triad, the Atma-buddhi-manas, is to be realised as separate from the mental body. That is the first step. You must be able to take up and lay down your mind as you do a tool, before it is of any use to consider the further progress of the Self in getting rid of its envelopes. Hence the mental body is taken as the starting point. Suppress thought. Quiet it. Still it.
Now what is the ordinary condition of the mental body? As you look upon that body from a higher plane, you see constant changes of colours playing in it. You find that they are sometimes initiated from within, sometimes from without. Sometimes a vibration from without has caused a change in consciousness, and a corresponding change in the colours in the mental body. If there is a change of consciousness, that causes vibration in the matter in which that consciousness is functioning. The mental body is a body of ever-changing hues and colours, never still, changing colour with swift rapidity throughout the whole of it. Yoga is the stopping of all these, the inhibition of vibrations and changes alike. Inhibition of the change of consciousness stops the vibration of the mental body; the checking of the vibration of the mental body checks the change in consciousness. In the mental body of a Master there is no change of colour save as initiated from within; no outward stimulus can produce any answer, any vibration, in that perfectly controlled mental body. The colour of the mental body of a Master is as moonlight on the rippling ocean. Within that whiteness of moon-like refulgence lie all possibilities of colour, but nothing in the outer world can make the faintest change of hue sweep over its steady radiance.
If a change of consciousness occurs within, then the change will send a wave of delicate hues over the mental body which responds only in colour to changes initiated from within and never to changes stimulated from without. His mental body is never His Self, but only His tool or instrument, which He can take up or lay down at His will. It is only an outer sheath that He uses when He needs to communicate with the lower world.
By that idea of the stopping of all changes of colour in the mental body you can realise what is meant by inhibition. The functions of mind are stopped in Yoga. You have to begin with your mental body. You have to learn how to stop the whole of those vibrations, how to make the mental body colourless, still and quiet, responsive only to the impulses that you choose to put upon it. How will you be able to tell when the mind is really coming under control, when it is no longer a part of your Self?
You will begin to realise this when you find that, by the action of your will, you can check the current of thought and hold the mind in perfect stillness. Sheath after sheath has to be transcended, and the proof of transcending is that it can no longer affect you. You can affect it, but it cannot affect you. The moment that nothing outside you can harass you, can stir the mind, the moment that the mind does not respond to the outer, save under your own impulse, then can you say of it: “This is not my Self.” It has become part of the outer, it can no longer be identified with the Self.
From this you pass on to the conquest of the causal body in a similar way. When the conquering of the causal body is complete then you go to the conquering of the Buddhic body. When mastery over the Buddhic body is complete, you pass on to the~conquest of the Atmic body.