Learn English – Meaning of “higher thought”

The word identity is being used here in something like its mathematical sense. That is to say that thought and being are inextricable, that they are in essence the same thing, that human thoughts are in some sense governed by the condition of being human animals who interact with the world around us with human senses and human means of locomotion, et cetera.

Identity, in this context, means sameness. In mathematical (and computing) use, things share an identity if they are precisely the same thing. Adding or subtracting zero, or multiplying or dividing by one are identity operations.

In common usage, we are often referring to a metaphorical "on paper" or conceptual representation of ourselves when we use the word identity. It isn't exactly who we are, but who we think we are, who others think we are, or the distorted picture of us created by the trails we leave behind.

This is not redundant; it removes some ambiguity. For example,

I thought that I left my keys on the table.

usually isn't really describing a specific thought - just a belief about what I did and where my keys are. But it could also mean - a definite thought passed through my mind, and that thought was "I left my keys on the table".

If I wanted to express the latter sense, I could make it clear by specifically saying something like

I thought to myself that I left my keys on the table.

which would generally mean that a definite thought passed through my mind.