There's a lot going down in this story. We have some weighty events and ideas to keep us awake at night. But we also see a more playful side of Hogwarts as we watch Harry and his friends fumble around with things like Apparition lessons, crushes, and parties. This levity balances the darker sides of the story, and we get the sense that the storyteller believes that where there is shadow, there might be light too.
Really stumped this time, Harry found nothing else to say. There did not seem to be any way Malfoy could have brought a dangerous or Dark object into the school. He looked hopefully at Ron, who was sitting with his arms folded, staring over at Lavender Brown.
"Can you think of any way Malfoy–?"
"Oh, drop it, Harry," said Ron.
"Listen, it's not my fault Slughorn invited Hermione and me to his stupid party, neither of us wanted to go, you know!' said Harry, firing up. (15.164)
Notice how the discussion went from Malfoy carrying a Dark object into school to Slughorn's party. We are constantly enveloped in this careful balance between threats of war and teenage growing pains.