What is, alone is what we refer to as Brahman, or Atma.
What is, is the non dual self alone.
However, this is not in our knowledge. In our knowledge, what IS, isnt one, but many.
We believe that each thing, has its own independent existence.
The tree exists, separate from the sky, separate from the earth.
While this is indeed true, but there is a greater truth to it, which we are not aware of.
That the tree, and the sky and the earth, are one and the same brahman, and only the gunAs or the attributes are different, that truth we are not aware of.
Reason is , we are not aware of the reality that , reality is non dual.
We are not aware, that this non dual reality is myself.
That atma, is brahman the non dual reality, which alone is in terms of forms and shapes, 'all that is here' that truth we dont know. ShAstra is the means of knowledge to know this.
To know that, the non dual brahman has a two fold nature.
It is attributeless, consciousness, and independent existence, that is the truth about brahman.
That it is the cause of the world, and from it arose the various manifest objects, and unto it the manifest objects resolve into unmanifest state, is looking at brahman in the form of maya shakti, that is what we call as mithya ( less true that satyam).
So what is true is what we want to know.