gof is turning point in the series not only because it plays a lot on horror tropes ( rowling is obviously influenced by stephen king and while that did have certain obvious elements in cos and poa, the beats hit in gof really drive it home ) but also because it brings a lot of social commentary into play that wasn’t necessarily there before. we got the backstory of blood purism, a bit more of the idealogy that surrounds it, and learned more about tom riddle as a person but gof really goes for it in terms of imagery and upping the stakes of those who believe in it.
what it also does is bring about harry’s central conflict and what sets him at odds with the villains of the series, and that’s his value of life vs their disregard for it. harry doesn’t view voldemort as his mortal enemy, at most he views him as someone to pity. a terrifying figure, a powerful wizard, but harry has more conflict with those who perpetuate the ideology he hides behind in the pursuit of acquiring power.
harry’s been confronted by tom’s disregard for people in the past ( mainly in cos ) but gof shows a side that’s less calculating. instead of using people for benefit, he tosses them aside for perceived lack of use.
harry’s dumbfounded by this. the image of cedric, devoid of all life with wide-open eyes, is something he is unable to shake. it reminds him of his parents, answering questions he had about the way in which they died. how quickly it moves in snuffing the light in someone out is startling ( to say the least ) to harry.
harry’s relationship with death until this point is loose. he hears his parents die in poa, and is greatly affected by their loss in his life, but he doesn’t really have a solid concept of it. there is comfort ( and horror ) in the knowledge dumbledore passes on, that his parents died loving him, and died leaving the mark of that love for him. there is cause, almost a sense of security. his parents death before, by the dursleys’, had been delivered to him as a senseless and random act. a fluke, at most. knowing that they died loving him as much as they did does offer some closure, though it never entirely makes sense to him ( upon seeing them through the stone he apologizes, more or less, for them dying for him ).
this brings us to cedric. he had no stakes in the game, there was no ( however orchestrated ) path of destiny pulling him in front of voldemort. the circumstances in which he died were random, he died senselessly because voldemort didn’t care. cedric could have just as easily survived the graveyard, the fact that he didn’t is a mere product of how callous and cruel voldemort is. his life is expendable, where as harry’s death is meant to be a fulfillment of destiny. harry has all sense of reason stripped away. as much as cedric’s unseeing eyes will haunt him.
cedric doesn’t die because he made a mistake, he doesn’t die in pursuit of a cause, he doesn’t die as a result of an accident. he’s murdered senselessly because the man directing his followers has no regard for life. - it’s a point made by dumbledore in his final address in gof, and immediately played on with the introduction of umbridge as a teacher.
the ministry’s cover-up of the events in little hangleton add insult on top of harry’s recovery from the brutal reality of watching someone die. it gets to the point where harry is infuriated by any inclination towards thought that he somehow deserved to survive, while cedric didn’t ( a fact highlighted in an outburst at ron and hermione ).
what harry finds intolerable is a disregard toward the right cedric had to live. because he didn’t deserve to be tossed in the middle of it all, he didn’t deserve to lose his life based on close proximity to harry, and he didn’t deserve to have his murder than be brushed off as a random force of nature that couldn’t have been prevented.
the fact that cedric died when adults could have prevented it matters, the fact that he was murdered by someone who held no value for life matters, and it sets harry on a path that is very clearly against the establishment put in place and then hidden behind by too many adults and those who follow cedric’s murderer.
cedric’s death not only shows harry exactly what he’s up against but also shows him, from every angle, what he can never become. dumbledore, again in that final speech, really sums it up. and in a way sums up what propels harry for the rest of the series.