1. Harry's Quidditch Match in "Half-Blood Prince":
* Why he plays: Harry is the Seeker for Gryffindor's Quidditch team and a key player. He feels a responsibility to his team and enjoys the sport. There's no specific dramatic reason he *has* to play in this particular match, it's just part of his normal routine.
* The significance: The match is actually a crucial plot point! It's during this game that Harry witnesses Draco Malfoy trying to use a curse on Ron Weasley, which later leads to the discovery of Sectumsempra and a deeper understanding of Draco's intentions. The Quidditch match is a crucial moment for Harry in the larger plot of "Half-Blood Prince."
2. Harry's Absence from the Final Quidditch Match in "Deathly Hallows":
* Why he doesn't play: Harry is not playing in the final Quidditch match because he is *not* in Hogwarts. He is on the run from Voldemort, along with Ron and Hermione, trying to find and destroy Horcruxes.
* The significance: The final Quidditch match is a symbolic moment, showing how far Harry has come from his carefree Hogwarts days. The sport now takes a backseat to the much larger battle for survival and freedom from Voldemort.
Let me know if you have any other questions!