On the ending of The Custom of the Country

1/ When Paul, now 9, visits the Moffatts’ new house, there is a very sad passage: 

“From these rooms Paul wandered downstairs again. The library attracted him most: there were rows and rows of books, bound in dim browns and golds, and old faded reds as rich as velvet: they all looked as if they might have had stories in them as splendid as their bindings. But the bookcases were closed with gilt trellising, and when Paul reached up to open one, a servant told him that Mr. Moffattt's secretary kept them locked because the books were too valuable to be taken down.” (Ch.46) 

And: 

“After a while he grew tired of watching the coming and going of white-sleeved footmen, and of listening to the butler's vociferated orders, and strayed back into the library. The habit of solitude had given him a passion for the printed page, and if he could have found a book anywhere—any kind of a book—he would have forgotten the long hours and the empty house. But the tables in the library held only massive unused inkstands and immense immaculate blotters; not a single volume had slipped its golden prison.” (ibid.) 

Is this not a vision of hell—a library full of books that can’t be read, and full of paper and ink that is never used? 

2/ At the end of the book, Paul is again uprooted, and forever lonely. It’s a poignant scene in the final chapter, where he doesn’t understand his mother’s marriages and tries to gather some facts about them from Mrs Heeny’s clippings. Edith Wharton is cruel indeed.

3/ I’m sure there are readers out there who sympathise with Undine Spragg. I don’t. 
She is shallow, ignorant, self-obsessed, and incapable of caring about anyone or seeing the meaning and value of anything. She contrasts nicely with Lily Bart of The House of Mirth—if Lily can’t bring herself to marry for money, Undine marries 4 times (I was mistaken earlier); if Lily finds it against her character to blackmail Bertha Dorset, Undine comfortably blackmails her own ex-husband; if Lily spends her little money paying back to Gus Trenor and paying all the bills, Undine doesn’t see why her father wants her to return the necklace to Peter Van Degen; if Lily loves Lawrence Selden, Undine doesn’t love anybody; etc. 
As a character, Undine is among the most well-drawn and vivid characters I’ve encountered in literature.   
See the way Wharton sums her up: 

“Even now, however, she was not always happy. She had everything she wanted, but she still felt, at times, that there were other things she might want if she knew about them.” (Ch.46) 

She can never be satisfied. The ending of the book is not the end. Having got everything, she’s still unhappy—her social success always ends in disillusionment.  

“There was a noise of motors backing and advancing in the court, and she heard the first voices on the stairs. She turned to give herself a last look in the glass, saw the blaze of her rubies, the glitter of her hair, and remembered the brilliant names on her list.
But under all the dazzle a tiny black cloud remained. She had learned that there was something she could never get, something that neither beauty nor influence nor millions could ever buy for her. She could never be an Ambassador's wife; and as she advanced to welcome her first guests she said to herself that it was the one part she was really made for.” (ibid.) 

Undine would never be satisfied. 
I started reading The Custom of the Country thinking it’s about a social climber who knows how to play the game and get everything she wants, but it turns out to be about a woman who keeps chasing false values and can never find contentment and happiness. 

4/ I’ve read reviews and articles about The Custom of the Country, and people usually say that Elmer Moffatt is Undine’s male counterpart. At the end she marries again her 1st husband, who is just like her and understands her.  

“Here was someone who spoke her language, who knew her meanings, who understood instinctively all the deep-seated wants for which her acquired vocabulary had no terms...” (Ch.41)  

In a way, he is her male counterpart. Both of them are pragmatic and opportunistic, both of them are social climbers, both of them can be selfish and ruthless (it is telling that Elmer Moffatt is the one to suggest the blackmail idea to Undine), both of them know what they want and succeed in getting it. 
But there are a few differences. 1st of all, Moffatt succeeds through business, through his own intelligence and personality, whereas Undine, as a woman, doesn’t have many options, and she succeeds through good looks and social instinct. Their difference can be best seen in a scene where Undine tries to persuade him to stay in France and be her lover but he refuses: 

“Feeling her power, she tried to temporize. "At least if you stayed we could be friends—I shouldn't feel so terribly alone."
He laughed impatiently. "Don't talk magazine stuff to me, Undine Spragg. I guess we want each other the same way. Only our ideas are different. You've got all muddled, living out here among a lot of loafers who call it a career to run round after every petticoat. I've got my job out at home, and I belong where my job is."
"Are you going to be tied to business all your life?" Her smile was faintly depreciatory.” (Ch.45) 

Undine has a lot more in common with him than with her previous husbands, but in this regard they are also incompatible. She can’t understand. 
Moreover, Elmer Moffatt, vulgar as he is, has an aesthetic sense that she lacks. It’s true that she loves dresses and jewellery, but I’m talking about an aesthetic sense for things that don’t go on her and make her more beautiful. She’s indifferent to the meaning and value of things—the same way she has Ralph’s family jewels reset, with no regard for the past, she sees Raymond’s family tapestries as nothing more than potential cash. If she’s incapable of understanding why Raymond doesn’t want to part with them, she’s also incapable of understanding why Elmer wants to possess them. 
He doesn’t read, and doesn’t know much about culture, but has the aesthetic sense to be a well-known collector. Because Elmer doesn’t have the good breeding of Ralph and Raymond, Undine can’t see that his mind too is superior to hers. 
Another difference is that I think Elmer Moffatt can be ruthless in business but still has his own kind of principle, and still has more kindness in him than Undine. He notices Paul whilst she neglects him. 
In the end, we don’t know what he thinks. But he would probably see Undine for what she is—she’s hollow. 

5/ This is another good book. I love Edith Wharton.