WARNING: This article contains SPOILERS for Spider-Man: Homecoming
The ending of Spider-Man: Homecoming directly affects Peter Parker's (Tom Holland) Marvel Cinematic Universe storyline going forward. It's been more than two years since Marvel Studios and Sony Pictures struck the deal that ushered Spider-Man into the MCU, with Holland making his official debut as Peter Parker in last year's Captain America: Civil War. Now, Holland's Peter Parker stars in his first solo MCU entry in Jon Watts' Spider-Man: Homecoming, the 16th movie in the cinematic universe and the second in Spider-Man's five-movie arc teased by Marvel Studios head Kevin Feige.
When Holland's Peter Parker was introduced in Civil War, he only briefly appeared in the film's overall runtime, but made a memorable impression on moviegoers. In terms of his storyline, Civil War bypassed the most well known aspects of Peter Parker's origin story, namely the death of his Uncle Ben and being bitten by a radioactive spider that grants him his abilities. When Tony Stark aka Iron Man (Robert Downey Jr.) plucks Peter from obscurity - his home of Queens, New York - the young superhero has been utilizing a homemade suit and webshooter. Tony gifts Peter with a high-tech suit and brings him to Germany to battle against Steve Rogers aka Captain America (Chris Evans).
Spider-Man: Homecoming picks up Peter's storyline prior to the events in which he appears in Civil War, with the young superhero documenting his trip to Germany with Tony and Happy Hogan (Jon Favreau) through a vlog. When Homecoming truly starts, Tony is dropping Peter back into obscurity with vague promises that the Avengers will call on Spider-Man when he's needed and until then, Happy will be Peter's liaison/handler. But, as Homecoming progresses, it becomes increasingly obvious that Tony planned on leaving Peter in Queens, encouraging him to tackle smaller level incidents, for the foreseeable future (though Marvel fans will no doubt know Tony will need to call on the web-slinging high school student come Avengers: Infinity War).
Although Peter spends much of Homecoming aspiring to become a full fledged member of the Avengers while largely ignoring his high school life and non-superhero future, he eventually learns the value of being a street-level hero in Queens. When Tony welcomes Peter to the Avengers estate in upstate New York and offers him a room and the opportunity to announce Spider-Man as an official member of Earth's Mightiest Heroes, Peter turns him down to remain in Queens. Of course, while Peter believes this to be a test, the audience learns Tony had every intention of publicly inducting Spider-Man into the Avengers. So, how does Peter's decision influence his MCU storyline and where exactly does Spider-Man go from here?
How Peter's Past Influences His Future
To understand where Peter goes next, we need to look back at Spider-Man's MCU arc so far. Unlike the majority of Marvel's other main heroes - with the exception of Guardians of the Galaxy - Spider-Man's story arc entirely revolves around the Avengers. Certainly, the formation and continuation of the Avengers is also important to the arcs of Iron Man, Captain America, Thor, Hulk, Black Widow, and Hawkeye as well as newer members like Scarlet Witch and Vision, but for these characters it's more of a day job or a concept with which they don't entirely agree.
For Peter Parker, his MCU superhero story begins when he's drawn into a conflict between members of the Avengers and he spends much of his time afterward thinking that joining the Earth's Mightiest Heroes up will be the pinnacle of his superhero career - and his entire life. It's a different, idealized perception of the Avengers that moviegoers haven't really seen portrayed in the MCU, since we've mostly followed members of the team and things always look different on the inside than on the outside. But, that's the intention of Spider-Man: Homecoming - to be a street-level superhero movie, and more specifically, to take Peter Parker from a massive Avengers-level conflict back to his neighborhood in Queens, portraying how that affects his growth as a hero.
In many ways, Homecoming forces Peter Parker back to basics. He goes from traveling to Germany for a single battle with the Avengers, to swinging through Queens thwarting bike thieves. Later in the movie, Tony takes away Peter's high-tech super-suit, forcing Peter to utilize his own pajama-like costume and homemade webshooters. It's a classic movie trope for the underdog to get back to basics in order to move forward, and that's exactly what happens with Peter in Homecoming. His final battle with Vulture using just his basic technology and suit helps him grow as a superhero since he isn't relying on Tony's technology and, for the first time in the film, he's trying to do the right thing for the sake of it, not as a way of being accepted by the Avengers. This marks his growth throughout Spider-Man: Homecoming, as evidenced by him passing on Tony's offer to join the Avengers.