Namaste,
Whenever God/Brahman is described, we find use of directly opposite entities that describe Him/It. In BG Lord Krishna says, "SadschAham Arjuna" ===> meaning I am Sat and also Asat. How can one entity be described by two exactly opposite entities ? How can He be both Sat and Asat simultaneously ?
What is Sat ? There are different meanings of Sat in different contexts but here Sat means "Existence" or "whatever exists". Accordingly, Asat is "whatever doesn't exist". So, what does that statement mean ? ===> I am both Existence and Non-existence !
This poses a logical paradox ! Anything which is existing can't be non-existent and whatever is non-existent can't be existing ! God Exists. He cannot be non-existent. Therefore, if He is also what is non-existing ... then does it mean that even non-existent things exist ?? Why such impossible combinations are needed to describe God ?
The problem comes because of our frame of reference from which we perceive "Existence" and "Non-existence". We first assume by default that "We Exist" and from that reference we perceive anything's existence or otherwise. Any perception is limited to our minds. Whatever is cognised by our sense organs or mind ( total 6 ) we perceive that is existing. Whatever cannot be cognised by our sense organs or even our mind is accordingly termed as "Non-existent". However, though our perception is dependent on Existence of an entity, Existence of an entity is not dependent on our perception or non-perception of that thing. ... and here lies the problem. God exists as perceptible entities and also what cannot be perceived by our mind. Why ? Because It is God alone that exists. Lord Krishna says in BG, "VAsudeva Sarvam Iti" and "SadschAham Arjuna !"
Now comes a natural doubt here. If something is Sat and also Asat ... is it Sat or Asat ? If something exists both as Sat and also Asat then for the sake of continuity the essence of what is both Sat and Asat must be something different from both Sat and Asat. This is because if anything can exist in two opposite things ... in reality it must be neither. Why ? Because when it is Sat then also its essence is same as when it was Asat and similarly, when it is Asat, its essence must be the same when it was Sat ===> In reality, the thing remains the same except its perceptible attributes. Therefore, It must be neither Sat nor Asat in essence.
This is why while describing Nirguna Brahman, God says in BG, Chapter 15, "Na Sat, Na Asat uchchyate" ===> This is called neither Sat nor Asat.
OM