Verse 18

18. Nonduality is indeed the highest reality; duality is spoken of as its outcome or, modification. For them (the dualists), exists duality in both ways; therefore or, with that Dvaita this (Advaita) does not conflict.

The statement "non-duality is indeed the highest reality" is based on the highest truth that The Self Alone Exists. This Self being Absolute is unchanging and complete. Where there is the perception of duality there will always be that that is incomplete. There will always be that to be desired, the present state will always need to lead to a completeness but through duality completeness is unachievable.
From Non-Duality can be imagined duality, that is duality can be superimposed on the Non-Dual substratum. But with the perception of duality Non-Duality cannot be imagined, that is Non-Duality, unity, is not imagined on the substratum of duality, two.
Non-Duality encompasses all and conflicts with none. It should also be remembered that these statements are not to say that there exists a choice between Non-Duality and duality. Non-Duality is the Reality. It is merely being shown how this truth is infinitely more desirable than the unreality of duality, which in itself is further proof of the truth of it, because it is due to living in ignorance of Advaita that all problems arise.