Themes are the fundamental and often universal ideas explored in a literary work.
Over and over again, Harry is forced to rely on the help and support of his two best friends, Ron and Hermione. When Ron and Hermione begin bickering, due in part to Hermione’s jealousy of Ron’s new girlfriend, Harry feels conflicted and upset by the possibility of losing his two companions. Likewise, when Harry develops feelings for Ron’s sister, Ginny, he stops himself from taking action too soon lest doing so should jeopardize his friendship with Ron. Even though the three teenagers are getting older, and encountering adult issues for the first time, they ultimately persevere, and at the close of Harry Potter and the Half-Blood Prince, Ron and Hermione vow to accompany Harry on his final quest to destroy Voldemort’s Horcruxes and, eventually, Voldemort himself. Harry accepts their offer, having by now learned that he cannot win this battle on his own.
Both Harry and Dumbledore find themselves constantly sacrificing their own peace and happiness for the greater good. Even though Harry would love to assume the life of a normal Hogwarts student, he understands that it is his destiny to fight and destroy Voldemort. Harry is perfectly willing to risk his own life to insure the safety of his friends. When Harry leaves with Dumbledore to collect what they think is a Horcrux, he leaves his vial of Felix Felicis with his friends to protect them should trouble arise. Likewise, Dumbledore is constantly willing to lay himself down to protect Harry and Hogwarts. When Harry and Dumbledore reach the basin containing the locket, Dumbledore drinks goblet after goblet of a poisonous potion, insisting that Harry continue to pour it into his protesting mouth, to retrieve and destroy the Horcrux and a piece of Voldemort’s soul.
Harry trusts his best friends without reservation and extends that same loyalty to Dumbledore, following his orders and trusting that Dumbledore is instructing Harry to do the right thing. Harry even tells the Minister of Magic that he is Dumbledore’s man through and through. The only issue on which Harry and Dumbledore fundamentally disagree is Dumbledore’s insistence that Snape can be trusted. Dumbledore will not tell Harry or any members of the Order of the Phoenix what it is about Snape that makes Dumbledore trust him so unconditionally, but he repeatedly tells Harry that Harry does need to worry about it. At the close of the book, when Snape murders Dumbledore, it is unclear as to whether Dumbledore has asked that Snape complete this task. Either way, Dumbledore has entrusted Snape with his life.