The entire veda is having only one goal which is revealing the reality that there is only one non-dual brahman. By knowing this fact one will be released from this life of becoming. Even karma-kanda (first portion of veda) which subject matter is dealing with worship, duty, and dharma where duality is involved, is there to prepare a mature thinking person for self-knowledge which is non-duality which is the subject matter of jñāna-kanda (end part of veda / vedānta).
What does it mean by non-duality? Everything here is only brahman. But this is not what we experience. We experience many-ness. These varieties of names and forms are called upādhi, because of which brahman appears as many, has attributes, and also limited. Just like light is recognised by us only when the light shines on an object. Through objects, the only one light appears as many, has attributes, and also limited. In the same manner, through the body of human being, we recognise consciousness brahman. This is called adhyaropa - superimposition. But we can't conclude the understanding of brahman in this manner, since human being is brahman, but brahman is not just human being only. Therefore apavāda - negation is to apply after adhyaropa. Ascertainment the existence of brahman which has no attribute through superimposition on upādhi, then negation of upādhi as being dependent existence (mithya) on satyam brahman to be exist, finally conclude that the very nature of entire name and form world is sat-cit-ānanda brahman alone.
Next, brahman doesn't just appear as the body and limbs of human being, but he also appears as attributes of organs of all.
sarvendriyaguṇābhāsaṁ sarvendriyavivarjitam | asaktaṁ sarvabhṛccaiva nirguṇaṁ guṇabhoktṛ ca ||13.14||
(That jñeyaṁ brahman) appears as one with attributes of organs, is free from all the organs, is unattached, is the sustainer of all, is free from the (three) qualities and is the experiencer of the (three) qualities.
We recognise the existence of consciousness though our mind and organs of senses. As we always say that we lost our consciousness when our senses and mind are suspended. It appears that consciousness is the attribute - guna of our organs, for us to recognise the existence of our organs. Actually it is the other way around, our organs and senses exist only because of existence consciousness. They are only the doorways / view points for us to indicate consciousness brahman. Therefore it is said here sarvendriyaguṇābhāsaṁ - in every expression of the eyes, ears, etc. brahman shines in that form. Previous verse said that brahman appears as all upādhi and here it is shown that he appears in the form of the upādhi-guna also. Even though brahman appears following the growth, contract, multiplication even destruction of body-mind-sense-complex (anukāritvād dehādi-vrdhi-sangkoca-ucchedādisu nāsesu ca), but by its own nature brahman is sarvendriyavivarjitam - free from all organs. That is why they are called upādhi, the attribute itself is kept changing. If the nature of the light is what we see, it will be the only thing we see (since satyam / the nature is changeless) and we will not see the light in the form of a pen, a book, etc. The light itself is free from attributes, but appears as them. In the same manner, brahman appears with the attributes of all senses and at the same time free from all of them. It is a paradox statement but the truth is such which can only be unfolded in this way. But these seemingly paradox statements are important to reveal the nature of infinite brahman which is not subject to time and space, yet upon which everything else depends for its existence. By adhyāropa - superimposing the attributes of all organs - sarvendriyaguṇābhāsaṁ, then apavāda - negation from all sense organs - sarvendriyavivarjitam, the truth of brahman is revealed.