Verse 18

18. What constitute the enjoyable,  the enjoyer,  and the enjoyment,  in the three abodes - different from them all am I,  the Witness,  the Pure Consciousness,  the Eternal Good the Sovereign Will.

"What constitute the enjoyable,  the enjoyer,  and the enjoyment,  in the three abodes"

If duality were true or possible then an enjoyable thing would have a traceable existence unlinked to anything else in existence.
Likewise the being who is the enjoyer would have a legitimate unique existence independent of any other.
So also would enjoyment itself have to lend itself to the experience of others because having its own existence would mean it was autonomous.

"different from them all am I,  the Witness"

With direct reference to "enjoyment" above this statement confirms that the Non-Dual Absolute Consciousness is That that is not one thing nor the other "different from them all am I" because the Absolute is the Singularity that is the witness and support for all the apparent diversity of creation.

"the Pure Consciousness,  the Eternal Good"

Being pure Consciousness of Absolute Knowledge Alone there is not that duality of another to deny the one intention.  The meaning is that the "Eternal Good" is all that Exists.  It is "good" because all must conform correctly to Absolute Knowledge because there is no other form of Existence.

"the Sovereign Will"

This statement confirms the fact of "eternal good" because here "Will" is formed of that very same Absolute Knowledge and there is none higher,  none lower and none other.

The three abodes (conscious states) themselves and all that arises within them are the creation of desire and therefore unreal,  this has been explained.
The meaning here is that you Alone really exist,  because you are the Solitary witnessing Consciousness of these experiences. 
Realising the Absolute as "I" all else can be allowed to fall away.  All that You Alone really are,  is the Absolute Alone.  Whatever else comes to mind can be let go of as unreal,  "that" that lets go can be surrendered because this verse tells us that your true being is pure Consciousness,  purely the witness.  By letting go of all concern for doing,  that eternal purity of Consciousness Alone remains.