"Most known motives are so suspect these days that I doubt whether the hidden ones are any better."
This quote speaks to how humanity has changed as the oceans receded and water became less readily available. Prior to the climate disaster, many people kept their negative and destructive motives kept hidden from other people and only expressed their more positive motives. Now, over the course of the novel in a time in which people are struggling to survive, humans still hide some of their motives. But instead of their known motives being more reasonable and positive, Ransom has observed that people's known motives are likely just as bad as their hidden motives.
"It seems we have a knack of turning everything we touch into sand and dust. We’ve even sown the sea with its own salt."
The sand mentioned in this quote is a metaphor for death and destruction. Because of human intervention and climate change caused by humans, the world has turned to sand and dust and effectively been destroyed. Humans have had a tremendous impact on the world, both positive and negative (but primarily negative). Because of human greed and consumption and pollution, the world is fundamentally worse off than before humans had the ability to alter the Earth.
"Five years earlier, when Ransom had spent his first weekends out on the lake, rebuilding his world from scratch from the materials of water, wind and sunlight, Philip Jordan had been the only person he could incorporate into his new continuum."
This quote gives more depth and character to Ransom, a man who like many others has struggled to survive in a world without an easily accessible supply of water. Ransom, like many other people, is not able to trust others because of their ulterior motives and their willingness to do whatever it takes to survive. After all, there isn't much water to go around and everyone in the world is trying the hardest they can to survive. To avoid pain and potential betrayal, Ransom decides to isolate himself and create as good of a world as he can for himself.
