The lines suggest a fall back into the laws of nature following the failure of human laws as seen in the novel.
Step-by-step explanation:
'The Road' is a post apocalyptic novel that develops an understanding that often the scientific method runs counter to the way human brain wants to work which is more in tune with the law of nature.
As all societal rules crumble and fail in the book, it is evident that all things greater than man, and by default older than man will survive him.
So the emphasis in this line is on older than man and mystery bath of which would have been understood had man not tried to conquer the world on his terms.