PraNAms.
It is like this. Neither body, mind or intellect (BMI) each by itself cannot know anything since each one is inert. On the other hand all pervading pure consciousness need not have to realize (or I should say realization has no meaning from its reference, since it is infinite).
When I say I know my body, mind and intellect, I, who is a conscious entity identifying with the mind, say that I am the BMI. It is not the mind making that statement since mind is inert, yet it is the mind making that statement, is it not? Without the mind, that is when I am in the deep sleep state, I cannot say I am BMI or cannot say anything. Thus the BMI are required for knowing or for self-realization. If I say I am not the mind, or I am not this, that negation is being done by who? Even that negation is done by the mind only, essentially mind is saying I am not the mind. Ego, in essence an identification with the mind as I am this, says that I am not this. This is the reasons why self-realization is very subtle process involving transcendence of the very process itself, since the process is time-bound. It is the same problem with respect to experience as self-realization.
Hence I have been trying to pointing out the subtleties involved and once one appreciates this, then one can easily understand what it involves. It is similar to the analogy of the seeing the light: here it is the light of consciousness. If you are in a room and light is all over the room, you can see the light only when the light falls on an object and the object reflects the light. If I stretch my hand, one see the hand only because the light is falling on it and getting reflected by it. Looking at the reflected light, I say I am seeing the hand. What I actually see is the light reflected by the hand, and not really the hand. I cannot see the back side of the hand, since the reflected light from the back side of my hand is not reaching my retina. Now the process of meditation involves understanding that the light is, rejecting it is not the hand, but shifting my attention to the light that is reflecting from the hand, because of which the hand is seen; know that alone is the light and not the hand that you see. If I remove the hand, I cannot see the light in the region or place where the hand was there before. Hence to see the light in the region where the hand was, I have to have a hand or object there so that I can see the light getting reflected and the reflected light I can see. Meditations is to reject that light is not the hand or the object, this, that is reflecting the light. The mechanism involving self-realization is exactly the same.
The thought flow is the mind. I can see the thought only when the light of consciousness falls on the thought and getting reflected by the thought. That constitutes the knowledge of the thought since I say I am conscious of the thought. Now meditation is, shifting my attention from the thought (object) but to that light of consciousness that is getting reflected by the very thought which is locussed on an object. Hence when I say I am not this, this is a thought, but I am that because of which the thought is seen. Without the thought, there may be silence, but I am 'seeing' or conscious of the silence (an object different from the seer or knower of the silence). Hence I am not the silence but that because of which I am conscious of the silence too. Hence the mind as an object is required for consciousness to reflect and I have to shift my attention of my mind to that because of which I am conscious of the mind (thoughts) too. Now if one asks, Who is seeing that light of consciousness reflecting in the mind?; it is again I, who is identifying with the mind, say that I am seeing the light of consciousness getting reflected by the mind. Hence Vedanta says, mind alone is the cause for bondage as well as for liberation - mana eva manushyaanaam karaNam bandha mokshayoH| - amRitabindu Upanishad.
Hope this helps.
Hari Om!
Sadananda