Question
How can Brahman/consciousness be all pervading including living and non living things?
Answer
Brahman is both the nimitta-kāraṇa (efficient cause) and upādāna-kāraṇa (material cause) of the universe. Otherwise, definition of Brahman is meaningless. If Brahman was not everything, then it would mean there is a second pole of power that Brahman has to contend with or be dependent on.
But as we see from Upanishads, Brahman is everything that exists.
Brhadaranyaka 1.4.10:
ब्रह्म वा इदमग्र आसीत् -- "Brahman indeed was all this in the beginning"
And Brahman became all the various differentiated aspects of the universe:
Taittiriya 3.1:
तस्माद्वा एतस्मादात्मन आकाशः संभूतः । आकाशाद्वायुः । वायोरग्निः । अग्नेरापः । अद्भ्यः पृथिवी । पृथिव्यामोषधयः । etc.
From this Atman, space came out, etc... all the way to earth, plants, humans, etc.
Taittiriya 3.6:
तत्सृष्ट्वा तदेवानुप्राविशत् । तदनुप्रविश्य सच्च त्यच्चाभवत् निरुक्तं चानिरुक्तं च निलयनं चानिलयनं च विज्ञानं चाविज्ञानं च ... ।
Having made it (the universe), he entered it... he became both gross and subtle, both well-defined and not-well-defined, both supporting and non-supporting, both conscious and non-conscious...
So by definition, Brahman expresses the nature of everything in the universe. So the meaning of "consciousness" in relation to Brahman's definition is not the narrow meaning as applicable to humans and animals.
This is the confusion that Maitreyi also had when Yajnavalkya was explaining Brahman to her.
Brhadaranyaka 2.4.13:
सा होवाच मैत्रेय्यत्रैव मा भगवानमूमुहन्न प्रेत्य संज्ञास्तीति स होवाच याज्ञवल्क्यो न वा अरेऽहं मोहं ब्रवीम्यलं वा अर इदं विज्ञानाय ।
Maitreyi said, "You confused me here, by saying that there is no consciousness after death." Yajnavalkya replied, "My dear, I haven't said anything confusing. It (Brahman) is quite complete in knowledge/awareness."
So, consciousness in humans is only one mode of Brahman. This is the mode that is available to us to realize Brahman.
In and by itself, Brahman, being everything, knows everything as itself, because there is nothing other than it. This is its mode as sat (existence) because it is everything that exists. Because it is everything that exists, it knows everything, because there is nothing left to know. This is its mode as cit (knowledge). These are mutually complementary.
The finer detail here is that existence implies knowledge and vice-versa. Because, even to recognize the state of non-existence, i.e. to say "nothing exists", there needs to be an observer that makes that observation. So absolute non-existence is impossible. Hence, the absolute existence and absolute knowledge of Brahman is logically self-evident.
Obviously, if Brahman is everything that exists, it is "all-pervading".
By realizing that our own innermost eternal reality is this Brahman, we become one with everything that exists. Obviously, our physical bodies are limited.
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