There is an opening here. It has methods of perception, eyes, ears, mouth, nose, touch. The opening has use of hands, arms, and legs for movement. It has a mind to use in pulling all this together. The mind extrapolates, comes to conclusions and reports back to that which is open. But what is it that is open? Everything listed above is for the use of that, but what is that?
The body is here, no doubt, with all these openings reporting. The mind is here and it is interpreting all the reports. But who, or what, are the body and mind reporting to? Even the mind knows that something is looking at it. Could it be that in the end, you cannot be defined by what the openings reveal, nor what definitions the mind creates?
You cannot put your finger, much less your mind, on what you are. You are an unknown. But there is no denying that you are here. All the openings reveal that you are here. The mind knows you are here. It just can't put it's finger on it.
What is looking through all these openings? There is an unknown here, always present, always aware. It knows that it is here. It knows that it is present. It knows the body, it knows the mind. But what is that?
This undefinable presence is known to be here, but it is not an object. It is the knower. Any of the millions of forms, with all their openings, open to this. This, that takes in all the knowing, all the perceptions, of all the forms. This is what you are. You are That.