Up to that point, the kind of explanation which explains things away may give us something, though at a heavy cost. But you cannot go on `explaining away' for ever: you will find that you have explained explanation itself away. You cannot go on `seeing through5 things for ever. The whole point of seeing through something is to see something through it. It is good that the window should be transparent, because the street or garden beyond it is opaque. How if you saw through the garden too? It is no use trying to `see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To `see through' all things is the same as not to see.
The Abolition of Man is not a novel. It's a collection of three essays that were derived from a series lectures Lewis presented. The book is only about 130 pages long (and the pages are fairly liberally margined), but it's full of content. To anyone used to reading Lewis' lighter theological works such as Mere Christianity or his fiction, the density of the text will probably come as a surprise. After all, it's not everyone who desires to read a hundred page dissertation on relative morality.
However, to reduce the book to another argument on relative-vs-absolute truth is to do it a disservice. Lewis looks at the problem from many angles and agrees that, while truth must be interpreted, there must exist a base truth, which he calls the Tao, from which other truth is derived. Interestingly when one considers Lewis' extensive apologetic work, Abolition is not a particularly Christian text at all, and Lewis mentions his personal beliefs only once, addressing what he assumes will be a common objection to his ideas.
Overall, the density of the book makes it hard to recommend to casual Lewis fans, but the whole thing is available online here, if anyone is interested.