This and thatness

The Hindu sages have a saying: "I am that, you are that, this is that, and that is all there is". That's true as far as thatness goes, and it helps to understand that there is only one soup, and we are all in it.
However, as well as that - the object - there is this - the subject that is viewing the object. Philosophically speaking, we have the seer and the seen, or if you like, the seer, the seen and the process of seeing. In Christian terms, the Father, Son and Holy Spirit.
How can you apply this in the moment? When you see your hand, who do you sense yourself to be: the hand, the observer of the hand, the process? You can see yourself as the seer - this - and soften your attachment to the unseen, as you unclench your hand. Whatever you can see is not you. As the unseen seer, and with the greatest of respect to the Hindu sages, we could assert that: really, there is only this.