This book serves as a big turning point in Harry’s life as well as the rest of the wizarding world.
First, Harry meets the very man (who as Voldemort is not so much a human anymore) who murdered both of his parents but failed to kill him. Even though Riddle fails to reincarnate himself, he comes very dangerously close to doing so. Harry sees the evil and intricacy of magic Tom Riddle used in school to become both the top wizarding student as well as the most terrible villain the magical world has seen so far. Through the diary and Ginny’s experience, Harry sees the wiliness of Riddle and the immense challenge he has to overcome to be the one that survives. In the first book, Harry only saw Professor Quirrell being possessed by Voldemort, but not the actual man (or quasi-man).
Second, we see a lot more of the class divisions that plague the wizarding world. The wealthy Malfoys have a particular grudge against the relatively poorer Weasleys. Harry has no parents, and so is seen a little as an outcast or just different, even though he has plenty of money. In addition, people discriminate between the purebloods, mudbloods, Muggles, squibs, and blood traitors. These divisions do little to help the wizarding world when battling Voldemort later in the series.
Third, the friendships we see Harry develop in the first book become much stronger in this second book. Trust is nearly broken in many situations, but these friendships and bonds survive another challenging year at Hogwarts. When Harry is hearing voices in the walls, he tries to deny it over and over because he is scared it will make him an outcast. When Ron and Hermione try to help him, he almost rejects them because he is confused at what is happening. When he accidentally speaks Parseltongue at the Dueling Club, his friends are the ones who stick with him while the rest of the school frames Harry as the Heir of Slytherin. These friendships and bonds help Harry get through his second year at Hogwarts.
Fourth, Harry again risks his life for one of his friends. Going into the deepest bowels of the school to find a monster who can kill with one glance to save a friend that may not be alive anymore, Harry again proves how worthy he is to be in Gryffindor. His loyalty and bravery complement each other as he battles the evil that already plagues his world.
Fifth, Harry is able to finally confess his fears and concerns to Dumbledore at the end. He expresses his worries that he may have been accidentally placed in Gryffindor, since the Sorting Hat did contemplate putting him in Slytherin. However, Dumbledore reassures Harry by telling him that choices define who we are and showing Harry that the sword had Godric Gryffindor’s name engraved on it.
This book provides hints at how deadly and treacherous Harry’s path will become as Voldemort becomes stronger and as Harry grows older. The war between good and evil will only escalate and kill the innocent as the Chosen One battles the embodiment of evil and hatred.