"Expelliarmus is a useful spell, Harry, but the Death Eaters seem to think it is your signature move, and I urge you not to let it become so!"
Lupin was making Harry feel idiotic, and yet there was still a grain of defiance inside him.
"I won't blast people out of my way just because they're there," said Harry. "That's Voldemort's job." (5.55)
Expelliarmus (the Disarming Spell) is Harry's signature move – and for a reason. As he comments, he's not willing to use violence against people who don't merit it, which displays the strength of character and sense of morality that Harry's developed over the past few years.
"Where no proven Wizarding ancestry exists, therefore, the so-called Muggle-born is likely to have obtained magical power by theft or force.
"The Ministry is determined to root out such usurpers of magical power…" (11.38)
Voldemort's desire to get rid of all non-pureblood Wizards is really a problem of identity – he's taken it upon himself to decide who is really a wizard and who isn't. However, there's the problem of personal identity – Muggle-born wizards really are just as magical as purebloods, and Voldemort's new restrictions are simply lies.
Harry drew closer, gazing up into his parents' faces. He had never imagined that there would be a statue. […] How strange it was to see himself represented in stone, a happy baby without a scar on his forehead… (16.57)
The sense of what might have been weighs heavily upon Harry in Godric's Hollow; he can't help but wonder what life would have been like if he wasn't the Chosen One. The image of himself as an infant seems particularly confusing – after all, what would Harry be like without his scar, without his mission?
He had spilled his own blood more times than he could count; he had lost all the bones in his right arm once; this journey had already given him scars to his chest and forearm to join those on his hand and forehead, but never, until this moment, had he felt himself to be fatally weakened, vulnerable, and naked, as though the best part of his magical power had been torn from him. (18.2)
Harry's wand is Harry, in his mind – and without it, he feels at a loss. This demonstrates how closely a wizard's wand is tied to his own personality; without the special wand that's seen him through encounters with Voldemort, he feels like he's not fully himself.
"…I'm as hunted quite as much as any goblin or elf, Griphook! I'm a Mudblood!"
"Don't call yourself –." Ron muttered.
"Why shouldn't I?" said Hermione. "Mudblood, and proud of it!" (24.87)
Hermione shows her strength and her confidence in her own identity here – she's not ashamed of her Muggle background, and she knows that it makes no difference to her Wizarding abilities.
"…Goblin notions of ownership, payment, and repayment are not the same as human ones. […] We are talking about a different kind of being," said Bill. "Dealings between wizards and goblins have been fraught for centuries. […] To a goblin, the rightful and true master of any object is the maker, not the purchaser. All goblin-made objects are, in goblin eyes, rightfully theirs." (25.93)
Bill reminds Harry that not everyone can be held to the same human standards – goblins have their own identity as a species, and thus live by their own rules.
"Karkaroff intends to flee if the Mark burns."
"Does he?" said Dumbledore softly… "And are you tempted to join him?"
"No," said Snape. […] "I am not such a coward."
"No," agreed Dumbledore. "You are a braver man by far than Igor Karkaroff. You know, I sometimes think we Sort too soon…" (33.144)
Dumbledore's comment that Hogwarts Sorts its students too soon implies that Snape's bravery should perhaps have placed him in Gryffindor – his true identity, which nobody else knows about, shows him to be as courageous and loyal as any true Gryffindor.
"Tell me one last thing," said Harry. "Is this real? Or has this been happening inside my head?"
Dumbledore beamed at him, and his voice sounded loud and strong in Harry's ears even though the bright mist was descending again, obscuring his figure.
"Of course it is happening inside your head, Harry, but why on earth should that mean that it is not real?" (35.96-98)
This is such a classic Dumbledore thing to say. It's a little trippy, a little goofy, and a little (OK, incredibly) deep and profound. Basically, he's telling Harry to trust what goes on inside his head – just because it's happening in there, doesn't mean it's imaginary or silly.
"So it all comes down to this, doesn't it?" whispered Harry. "Does the wand in your hand know its last master was Disarmed? Because if it does… I am the true master of the Elder Wand."
A red-gold glow burst suddenly across the enchanted sky above them as an edge of dazzling sun appeared over the sill of the nearest window. The light hit both of their faces at the same time, so that Voldemort's was suddenly a flaming blur. Harry heard the high voice shriek as he too yelled his best hope to the heavens, pointing Draco's wand:
"Avada Kedavra!" "Expelliarmus!" (36.118-121)
Harry stays true to himself all the way to the end – he recognizes his own identity as the master of the Hallows, and pulls out his signature spell to prove it. Voldemort's own actions are classic Voldy; he thinks he can just blast Harry away and solve all his problems, but this single-minded attitude fails him here. (Hasn't he yet learned he can't use that spell on Harry, by the way? Sheesh.)
"If there was one place that was really important to You-Know-Who, it was Hogwarts!"
"Oh, come on," scoffed Ron. "His school?"
"Yeah, his school! It was his first real home, the place that meant he was special; it meant everything to him, and even after he left –."
"This is You-Know-Who we're talking about, right? Not you?" inquired Ron. (15.23)
The similarities between Harry and Voldemort seem to be too much at times – they make Harry capable of understanding the evil wizard better than anyone else can, but they also make for an uncanny crossover between the two.