it wasn't, and you were in the only nice, dry, cozy place in the world. I loved that damn museum.

Holden loves the museum because there is a permanence to it:

...in that museum was that everything always stayed right where it was. Nobody’d move. ... Nobody’d be different. The only thing that would be different would be you.

In his angst, Holden cannot fail to recognize the impermanence of life, something that has been tragically proven by his brother Allie's death and the death of James Castle, who could only fight against the other boys by jumping to his death.  

In the museum, the encased Eskimo prompts Holden to think that

...certain things...should stay the way they are. You ought to be able to stick them in one of those big cases and just leave them alone.

This is the idea that Holden ponders as he leaves the museum and walks around.

The museum represents childhood memories of school field trips for Holden, reminding him of a time in his life when things were simpler and when he was happier.  Allie, his younger brother, was still alive then and all in all his family was much happier as well.  More importantly, however, the museum is a place that never experiences change. This also is important to Holden because all the change he has experienced in his life has been negative: his brother Allie's death, the effects that death has had on his family and friends, the effects on his academic progress, his repeated expulsions from schools and his having to become accustomed to more new people, etc.

Holden Caulfield has experienced several traumatic events as an adolescent, and throughout the novel, he struggles to cope with his difficult feelings. Holden is particularly afraid of growing up and becoming an adult. He views every adult as a "phony" and desperately desires to remain an adolescent. Holden's fear of the future enhances his fondness for the past, and he reminisces about his pleasant experiences as a child visiting the Museum of Natural History. As Holden remembers his enjoyable childhood experiences at the museum, he says,

The best thing, though, in that museum was that everything always stayed right where it was.

Holden's comments reveal his attachment to the past, which is connected to his relationship with his deceased brother, Allie. Holden has never properly coped with Allie's death and struggles to move on with his life. His fondness for the past is directly associated with his feelings for his younger brother and fear of entering the adult world. Holden expresses his desire to remain in the past, where everything stays the same and is untainted, by saying,

Certain things they should stay the way they are. You ought to be able to stick them in one of those big glass cases and just leave them alone. I know that's impossible, but it's too bad anyway. Anyway, I kept thinking about all that while I walked.

Overall, Holden enjoys the fact that the exhibits in the Museum of Natural History remain the same and never change, which is how he wishes life worked. Holden inherently desires to remain an adolescent and never change, like the permanent exhibits inside the glass cases; he fears the future and wants to remain young and innocent.

Two famous New York museums play a part in The Catcher in the Rye: the Museum of Natural History and the Metropolitan Museum of Art.

Holden has happy memories as he anticipates visiting the Museum of Natural History. He often went there as a child. It was a point of stability for him, because nothing ever changed. The dioramas of Eskimo and Indian life were always the same every year, as was the film about Christopher Columbus. Holden associates the museum with his secure childhood before his brother's death. He ruminates that:

Certain things they should stay the way they are. You ought to be able to stick them in one of those big glass cases and just leave them alone. I know that's impossible, but it's too bad anyway.

However, when he arrives at the museum, he decides not to enter. It's very likely that he doesn't want to risk having his pristine childhood memories ruined:

Then a funny thing happened. When I got to the museum, all of a sudden I wouldn't have gone inside for a million bucks. It just didn't appeal to me--and here I'd walked through the whole goddam park and looked forward to it and all. If Phoebe'd been there, I probably would have, but she wasn't. So all I did, in front of the museum, was get a cab and go down to the Biltmore.

Later, he tells Phoebe to meet him at the "museum of art." From the description he offers, he means the Metropolitan Museum of Art. While waiting for Phoebe, he helps two boys who are playing hookey from school find the "mummy" exhibit, which involves walking through the reconstructed walls of a pyramid. The boys get frightened and run off, but Holden continues. He is disillusioned, however, when he notes someone has written an obscenity on a wall: this is the kind of shock he no doubt wanted to avoid by not entering the Museum of Natural History.

Museums represent safety, childhood, and happy memories to Holden, which is why he likes the Museum of Natural History. But as he finds out at the Metropolitan Museum of Art, even museums, like so much else, can force him to confront a loss of innocence.

"The best thing, though, in that museum was that everything always stayed right where it was. Nobody'd move."

Holden likes the static nature of the museum.  He likes the fact that the exhibits stay the same.  It feels comfortable and familiar to him.  He likes the unchanging nature of the museum, because it is so different than what he is experiencing on a personal and real life level.  His happy childhood is no longer, because he is growing up.  His brother died years before, and Holden's entire family dynamic has changed.  School is changing for Holden too.  Classes are getting tougher, and he just can't seem to stay in school.  Holden is scared by all of the change that he sees happening around him, and he wishes that life could be more like the museum.  Static, predictable, unchanging, and comforting.  I have to admit, while I don't like Holden that much through most of the book, I sometimes completely agree with Holden's attitude on this one.  

Holden is a troubled adolescent struggling to find himself after the traumatic death of his younger brother, but his attitude toward money reflects the complete carelessness of a person who has always had it.

Holden describes his father as wealthy corporate lawyer who invests in Broadway shows and "really hauls it in." Holden lives in a milieu of country clubs, expensive boarding schools, and upper Manhattan apartments. He knows things that mark him as upper class, such as that you don't order a Tom Collins in winter. He has on hand a lot of money for a 16-year-old, enough to finance a spree in New York City that includes a stay at a hotel, cab rides, expensive drink tabs, hiring a prostitute he doesn't have the heart to sleep with because she's so young, and meals out without a concern for spending. He notes that this is in part because his grandmother sends him birthday money about four times a year.

When he gives ten dollars to the nuns he meets while eating breakfast in a diner, it is because he feels guilty that he has just eaten a full meal of just about everything he could order while they are dining meagerly. Ten dollars would be about the equivalent of $100 in today's money, so he has the ability to give out money generously.

Holden, however, finds money oppressive. After he gives the nuns $10 when he wishes he could have given them more, he curses money and says it makes him feel "blue as hell" because he has already committed to spending a lot on a frivolous date with Sally. He intuits the unfair privilege wealth gives him, saying:

In New York, boy, money really talks—I'm not kidding.

Holden both accepts and is made uncomfortable by the power wealth affords him. It's worth noting, too, given the book's chronology, set in the late 1940s, that Holden would have grown up in the Great Depression and World War II, making his careless spending all the more noticeable to an early generation of readers scarred by the deprivations of the Depression and still remembering the constraints of war rationing.

In The Catcher in the Rye, Holden has a very casual relationship with money. He often spends it easily and thoughtlessly, yet at the same time he often seems to feel scornful of money. Here is one passage we can look at where Holden extensively describes his feelings toward money:

"While I was in the cab, I took out my wallet and sort of counted my money. I don't remember exactly what I had left, but it was no fortune or anything. I'd spent a king's ransom in about two lousy weeks. I really had. I'm a goddam spendthrift at heart. What I don't spend, I lose. Half the time I sort of even forget to pick up my change, at restaurants and night clubs and all. It drives my parents crazy. You can't blame them. My father's quite wealthy, though."

What we can gather from this passage is that Holden comes from a wealthy family and has always had what he needed and never wanted for anything; therefore, he doesn't need to worry about how much money he spends because he will always be able to get more. As he says, he is a "spendthrift," an extravagant squanderer of money. However, even though Holden doesn't need to worry about money, he recognizes that money doesn't necessarily make one happy. He says, "Goddam money. It always ends up making you blue as hell." It seems that whether Holden has money or doesn't or gives it away, it makes him sad.

Yet another example of Holden being careless with money is when he quite literally throws it away:

"I took out my dough and tried to count it in the lousy light from the street lamp. All I had was three singles and five quarters and a nickel left--boy, I spent a fortune since I left Pencey. Then what I did, I went down near the lagoon and I sort of skipped the quarters and the nickel across it, where it wasn't frozen. I don't know why I did it, but I did it."

He has almost no money left, yet from what he has, he throws the coins into the lake. Holden has a very immature and realistic relationship with money.

For Holden Caulfield, the best thing about the Museum of Natural History is "that museum was that everything always stayed right where it was."

He adds the following:

"You could go there a hundred thousand times, and that Eskimo would still be just finished catching those two fish, the birds would still be on their way south, the deers would still be drinking out of that water hole ... Nobody'd be different. The only thing that would be different would be you. Not that you'd be so much older or anything. It wouldn't be that exactly. You'd just be different, that's all."

This contributes to one of the novel's overall motifs: Holden's fear of change. Throughout the novel, Holden attempts to protect the children around him, particularly Phoebe. In fact, the title of the novel The Catcher in the Rye is an ironic mistake by Holden. Holden mistakes the words in the poem, which say "If a body MEET a body coming through the rye" and replaces this with "catches." Then Holden goes on to explain that he wants to be the one who "catches" kids before they fall off a cliff. This is ironic because the poem is about a boy and girl meeting out in a field of rye to probably have sex, something Holden seems deathly afraid of.

The reason this relates to the museum is that everything in the museum is preserved. Holden does not have to do any "catching" here.

Holden's attitude towards money reeks of hypocrisy, for example, he resents the adults that he characterizes as phonies who spend their time pursuing financial success.  One such adult is a patron of Pencey Prep Mr. Ossenburger.  Holden lived in the Ossenburger Memorial Wing of the dorms at Pencey.  Mr. Ossenburger is a Funeral Director.

"He made a pot of dough in the undertaking business after he got out of Pencey.  What he did, he started these undertaking parlors all over the country.  You should see old Ossenburger.  He probably shoves them in a sack and dumps them in the river.  He gave Pencey a pile o dough and they named our wing after him.  He came up to the school in this bitg goddam Cadillac and we had to stand up in the grandstand and give him a locomotive, that's a cheer." (Salinger)

Holden mocks Mr. Ossenburger and disrespects the fact that he has made a successful living in the funeral business.  He also disrespects his own grandmother, when he says that she sends him money four times a year, for his birthday.

"I have a grandmother that's quite lavish with her dough.  She doesn't have all her marbles any more, she's old as hell and she keeps sending me money for my birthday about four times a year.  Anyway, even though I was pretty loaded, I figured I could always use a few extra bucks." (Salinger)

Holden comes from a financially wealthy family, therefore he does not have to think about money, because his family provides it for him.  He has no respect for the money his parents have paid for his prep school tuition, he keeps getting kicked out of one school after another, giving no particular attention to his academic pursuits, not caring that his parents are wasting money.

Holden seems to resent the process of earning money, yet he has a pocketful of money that his grandmother has given him, without which, he would not have been able to travel to NYC by himself, escaping the confines of Pencey after he learned that he was expelled.

As a post-WWII novel, Salinger could be expressing his resentment of the explosion of prosperity that American experienced in the years following the war.  There was an economic boom, and Holden equates money with phoniness, and adults have jobs and make money.

This ties in with Holden's real problem his desire to remain in childhood and avoid becoming an adult.  He prefers the safe comforts of childhood, free of responsibility, unencumbered by obligation, being taken care of by others, including phony adults, who need to make money to meet their obligations. Holden takes his childhood obsession a step too far, he also rejects his responsibility to be academically successful, even children are expected to succeed in school.