Big changes made by Gatsby relate to his parties and to Daisy. This chapter opens with the news that "the lights in [Gatsby's] house failed to go on one Saturday night" and the parties at the mansion had ceased. At this point, the purpose of the parties has been fulfilled. Gatsby has re-connected with Daisy, impressed her with his achievement of wealth, and is now engaged in an affair with her that he hopes will lead to marriage.
Gatsby's aim in throwing the parties in the first place was to do just this, to capture Daisy's attention and her love.
The shift, the change, from huge and elaborate parties to a new, far quieter lifestyle is rather drastic. Nick takes notice of the lightless mansion and asks after Gatsby, inquiring of "an unfamiliar butler" as to whether or not Gatsby was sick. When Nick finds out that Gatsby has fired all of his former servants, Nick wonders if Gatsby is going away and puts this question to him over the phone.
During this phone call Gatsby's motives are explained: he says that he ans Daisy are meeting, which implies the need for secrecy.
"Daisy comes over quite often - in the afternoons."
Nick suspects that Daisy did not approve of the parties, but Gatsby speaks to the idea of discretion in his decision to fire his staff and to end the stream of Saturday night parties. Gatsby does not want people to gossip about Daisy's visits. She is, after all, a married woman of wealth and social standing with a public profile.
With his aims nearly attained, Gatsby transitions from a very public attempt at courtship to a very private affair carried on with Daisy.
Gatsby makes changes to his lifestyle when he stops having his enormous parties, for one thing. He also fires all his servants and replaces them with new ones recommended to him by Wolfsheim. In short, his house has gone from being almost a public amusement ground to being a forbidding fortress. Nick at first has no idea that these changes have happened: when he calls at Gatsby's house to inquire if he is sick, the new butler is quite rude:
“Is Mr. Gatsby sick?”
“Nope.” After a pause he added “sir” in a dilatory, grudging way.
“I hadn’t seen him around, and I was rather worried. Tell him Mr. Carraway came over.”
“Who?” he demanded rudely.
“Carraway. All right, I’ll tell him.” Abruptly he slammed the door.
When Nick does talk to Gatsby, Gatsby explains that he wanted servants who "wouldn't gossip," adding that "Daisy comes over quite often—in the afternoons." Gatsby's changes are motivated by his desire to protect Daisy; now that he has her, he does not want her to be found out and disgraced; he wants to protect her until they act as a couple and part from Tom, which he learns will never happen.
At the beginning of the chapter, Nick discovers that Gatsby has dismissed his servants so they can't see what Daisy and Gatsby do during her afternoon visits to his mansion. During the trip to New York, Gatsby tries to force Daisy’s hand by telling Tom that she had never loved him and violent emotions erupt driving Tom to call Gatsby all sorts of names.
After the group leaves New York, Nick finds out about the death of Myrtle and the fact that Daisy was driving but Gatsby was taking the blame. Daisy is totally unappreciative of his self-sacrificing protection and sits with Tom at the table, preparing herself for her safe retreat into her insulated society.
Nick walks away to a waiting taxi and watches Gatsby stand "in the moonlight—watching over nothing," not knowing Daisy has left already. This scene recalls the first chapter of the book where Nick watches Gatsby look across the water to the green light opposite.
Nick recognizes that, as a symbol for American Dream, Daisy is inadequate, unworthy. Gatsby has emotionally expended everything to attain her; now, all he has left of her is like “"—watching over nothing." Unfortunately, Gatsby is not yet ready to see this revelation and will continue his obsession with "nothing."
As things turn out, the changes to Gatsby's lifestyle, which concern Nick, that were made to protect Daisy, leave Gatsby protecting no one, even though he ironically becomes her ultimate protector by unintentionally being the recipient of the punishment belonging rightly to Daisy.