Muggles' Guide to Harry Potter/Books/Philosopher's Stone/Chapter 7

Synopsis.
Upon reaching the castle, Hagrid hands the new students over to Professor McGonagall. Before the ceremony begins, Professor McGonagall briefly explains about the four Houses the students will be sorted into, as well as House Points. Points will be earned based on a students best performance or "triumphs", whereas points will be deducted for breaking any rules. Whichever House has the most points by the end of the school year wins the House Cup. In an anteroom, the students nervously wait to be sorted into school Houses. The Ghosts passing through the anteroom make Harry even more nervous. Professor McGonagall then leads them into the Great Hall, and in turn, the Sorting Hat calls out which House each student is assigned to. There are four Houses, each with specific characteristics. Slytherin is filled with ambitious, cunning witches and wizards; Ravenclaw is home to the most intelligent; Gryffindor houses only the brave; and Hufflepuff is where the most fair and honest go. It is Harry's turn, and he sits on the stool and the Sorting Hat is placed on his head; the Hat suggests quietly that Harry's intelligence, talent, and his urge to prove himself could make him great. But Harry balks when the Hat suggests Slytherin, so it instead places him in Gryffindor House. Ron and Hermione also are Sorted into Gryffindor, as well as: Neville, the boy who lost his toad; Seamus Finnigan; and Dean Thomas, who is mentioned in the US editions as being a "tall, black boy," but is not described in the book's British editions. Draco Malfoy is sorted into Slytherin. Neville later tells Harry that his family had believed he had no magical power at all until he was able to survive being dropped out of a window.
Professor Dumbledore then makes a few eccentric prefatory remarks, and the feast begins. During the feast the Gryffindor House ghost, Sir Nicholas de Mimsy-Porpington, appears. The older students know him better as Nearly Headless Nick, due to his partially severed neck that barely tethers his head to his body. As Harry scans the teacher's table, his scar throbs with pain when he sees Professor Snape, the Potions teacher, scrutinizing him. One additional Dumbledore announcement catches Harry's ear: "this year, the third floor corridor on the right-hand side is out of bounds to everyone who does not wish to die a very painful death." Harry asks Percy if Dumbledore is serious, and Percy replies that he must be.
As Percy leads the first-year Gryffindors on a convoluted path through the castle's many corridors, the wall paintings' occupants comment on the passing students. Peeves, a Poltergeist, briefly harasses them. Eventually they reach the entrance to Gryffindor tower, guarded by a portrait of a fat lady. Percy gives the password ("Caput Draconis"), and everyone heads into the common room and to their dormitories. During the night, Harry dreams about Quirrell's turban telling him he must transfer to Slytherin because it "is his destiny." The turban started to tighten on his head. Draco Malfoy then appeared laughing at Harry trying to take off the turban. By the next morning, Harry has forgotten the dream.
Analysis.
Hogwarts castle and its four Houses, Ravenclaw, Hufflepuff, Slytherin, and Gryffindor are introduced; we are also served our first taste of the rather eccentric Headmaster, Albus Dumbledore (who Harry thinks might be slightly mad), while Harry's scar may be acting as a barometer to the passing scene. Harry's fame in the Wizarding world is also further shown through the other students' excited responses to his name being called out for Sorting.
The Sorting ceremony is arguably the most important school rite that Hogwarts students participate in. It not only determines in which House they will spend their entire seven years at Hogwarts, but it reflects much about who they are and generally indicates what direction their lives may take. They will also be affected by others in their own House. These affiliations will build life-long alliances, as well as create ongoing rivalries among the Houses, though these are generally friendly; there is, however, a particular competitiveness between Gryffindor and Slytherin, two Houses that will symbolize themes of good and evil in the series, and which path—light or dark—a character chooses to follow. The four Houses are distinct and represent the individual school founders: Helga Hufflepuff, Salazar Slytherin, Rowena Ravenclaw, and Godric Gryffindor. All had varying talents and differing views, and students with similar characteristics to the founders are usually sorted into the House that best reflects those traits. The Hat sees abilities in Harry–cleverness, determination, and ambition–that align with Slytherin, and could lead him to greatness, something no one has ever told Harry or that he considered about himself. Some students, like Harry, do appear to have traits suitable to more than one House, and the Sorting Hat mulls over where it should place him. Already dismayed by his connection to Voldemort, Harry immediately resists Slytherin, a House he knows is associated with Dark Wizards, as well as unpleasant students such as Draco Malfoy. 
Although the Sorting Hat apparently favors putting Harry in Slytherin House, he is, of course, equally well suited to Gryffindor, which is noted for nobility and bravery, and, in many ways, seemingly opposite to Slytherin. Also, Harry's parents were both Gryffindors. Harry has certainly shown he is noble, and has already demonstrated much courage in his young life, first by standing up to the Dursleys, then by entering a strange, unknown world, and now, as he challenges the Sorting Hat. Rather than passively waiting for it to make its selection, he specifically requests not to be sorted into Slytherin. Most students probably never question or oppose which House they are assigned, and though the Hat senses Harry's talents are suitable to Slytherin, it never forces a choice on him. Instead, it entices Harry by wondering where it should place him. Harry's request shows his growing ability to consider all options and make his own decisions based on that. Even if fate has decreed that he is to one day challenge Voldemort, Harry possesses the power to affect that fate by his own design. This trait is re-emphasized in the next book and throughout the series. After some negotiating, the Hat places him in Gryffindor. It should be noted that Harry never actually requested to be in Gryffindor or the other Houses, rather he chose not to be sorted into Slytherin, a House that, to him, represents a dark path. 
Despite its dark reputation, Slytherin House is not inherently evil, nor are all its students so unpleasant as Draco Malfoy and his cronies. However, that particular House does represent certain characteristics, such as ambition, power-hunger, shrewdness, slyness, etc., that Dark Wizards apparently possess in abundance. Like Harry, all Slytherins have a choice as to how they will utilize these traits and whether they will follow a light or dark path. Later in the series, a Slytherin character becomes Harry's ally.
Dumbledore's stern warning that the third-floor corridor is off limits, in addition to the package Hagrid delivered, indicates that unusual, and possibly sinister, events may be unfolding at Hogwarts. The break-in at Gringotts may be related, though Harry cannot be certain; it caught his attention purely because he had visited Gringotts a little over a month ago. Harry is beginning to tie these clues together, already suspecting that whatever Hagrid took from Gringotts is what is now being guarded on the third floor. The pain in Harry's scar when Professor Snape looks at him also convinces Harry that Snape is somehow connected to all this. Harry's keen observation and inquisitive nature are becoming apparent here, and throughout the series, he will continually need to piece information together to solve even bigger puzzles, often risking his life in the process. However, his conclusions are sometimes wrong or will lead him in the wrong direction, while his immaturity, bias, and innate stubbornness often prevent him from considering more reasonable alternatives. 
Ideas are also presented on how the Wizarding realm differs from the Muggle world in which Harry had been trapped until now. Understanding how Wizard society operates here is not only appropriate for Harry's age (eleven), but also the details are presented in a comprehensible manner suitable for someone at that age level who is suddenly thrust into a magical world that they never knew existed. For instance, when the banquet food appears on the plates, Harry never considers who prepared it or how it got placed there. That curiosity and the resultant understanding comes in about another three years.
Harry's dream is foreshadowing this book's main plot line. The reader still knows too little to interpret this dream, but may understand that there is some connection between Quirrell's turban and the pain in Harry's scar.
Greater Picture.
The byplay between Harry and the Sorting Hat becomes more germane in the second book, "Harry Potter and the Chamber of Secrets", and later in illustrating the differences between Harry and Voldemort. While the Hat recognizes qualities in Harry that were unknowingly bestowed on him by a connection between him and Voldemort, it is ultimately Harry exercising his independent choice and free will that leads to him being assigned to Gryffindor. It is interesting to consider whether or not the Sorting Hat would still have considered Slytherin for Harry if this connection between him and Voldemort had never existed. 
As noted in the above analysis, not all Slytherins are evil. Professor Horace Slughorn, a Hogwarts teacher who first appears in "Harry Potter and the Half-Blood Prince", is also a Slytherin. He becomes Slytherin's House Head after Professor Snape apparently defects to Voldemort's side. And though Slughorn possesses many typical Slytherin traits, he always follows a light path, rejecting Voldemort's beliefs, and aligns himself with Dumbledore and Harry. 
It is learned later in the series that Sirius Black, Harry's godfather, was also sorted into Gryffindor, even though his family is primarily sorted into Slytherin House and some are or were affiliated with Lord Voldemort. We do not know whether Sirius, who rejected his family's pure-blood beliefs and eventually became estranged from them, chose not to be placed in Slytherin, though we will learn that he stated a preference for Gryffindor before his own Sorting. It is possible that he, like Harry, refused the Sorting Hat's initial placement, but equally it is possible that the Hat placed him in Gryffindor of its own accord.
We are meant to believe that the exploding pain in Harry's scar is because Snape is staring at him. It is true that Snape is displeased to see him; at that distance, Snape can only see the resemblance between Harry and his father James. We learn later that James and Snape were in the same year at Hogwarts, and they were bitter antagonists. The pain in Harry's scar is because Voldemort, then riding on Quirrell's head, is either looking at Harry through Quirrell's turban, or is using Legilimency to observe the room, and has just detected Harry.
Harry's scar did not hurt when he first met Quirrell in the Leaky Cauldron, nor did Quirrell's skin burn when they shook hands there (see The Man with Two Faces), because he was not wearing the turban at the time, and hence Voldemort was not possessing him from the back of his head. Quoting from the text, at the welcoming feast, "Harry spotted Quirrell, too, the nervous young man from from the Leaky Cauldron. "He was looking very peculiar in a large purple turban."" (Emphasis ours.) This implies that this is the first time Harry has seen him wearing a turban.
We will learn later that the same Gringotts vault that Hagrid removed the small parcel from is the one reported as being recently broken into, which of course only adds to the mystery. We should note that Harry's visit to Gringotts is actually further in the past than it currently feels. It was on Harry's birthday, July 31, that Hagrid took Harry to Diagon Alley, and we read about the break-in at Gringotts on the Hogwarts Express, on September 1; the entire month of August falls between the two occurrences.
Harry's dream may actually foreshadow events in the entire series, rather than in just this book. It could also be an unconscious attempt by Voldemort to influence Harry's actions using Legilimency, as he will in "Harry Potter and the Order of the Phoenix". While this is neither confirmed nor refuted by later events, it is unlikely that Voldemort was consciously using Legilimency; Voldemort started deliberately using Legilimency on Harry after he learned there was an existing connection at about Christmas in "Harry Potter and the Order of the Phoenix". We do learn later in the series, however, that Harry gains the ability to tune into Voldemort's thoughts at will without the Dark Lord being aware. This may be an early incident where neither Harry nor Voldemort are aware it is happening.
There is also half a timeline contradiction in this book. At Nearly Headless Nick's deathday party, commemorating the five-hundredth anniversary of his death, in "Harry Potter and the Chamber of Secrets", his death is stated to have been on 1492-10-31. However, in this chapter, Nearly Headless Nick states that he has been dead for nearly 400 years. It is assumed that this is an error by the author, which was changed in later editions by having Nick say that he has been dead for nearly 500 years.
As mentioned in the Greater Picture section for that Deathday Party chapter, Nearly Headless Nick's death date can determine a timeline for the entire series, leading us to all the book's specific dates. However, this timeline is not critical to this series plot or events, as it only affects the interactions between events in the books and the Muggle world, which are few.
The other teachers' reaction to Dumbledore's announcing the School Song has led many fan sites to question whether its failure to appear in subsequent volumes was due to the teachers rebelling against it. The author has said that "Dumbledore called for the school song when he was feeling particularly buoyant, but times are becoming ever darker in the Wizarding world." It is also true that the School Song, which was entertaining when we heard it initially, would not be equally so if it was re-introduced. This also may be the reason that we so seldom are present at the Sorting, to keep the Hat's annual song from becoming tedious.