HARRY: And what do you know about the Deathly Hallows?
OLLIVANDER: It is rumored there are three: The Elder Wand, the Cloak of Invisibility, to hide you from your enemies, and the Resurrection Stone, to bring back loved ones from the dead. Together, they make one the Master of Death. But, few truly believe that such objects exist.
The Resurrection Stone is kind of dangerous, since it allows you to bring back dearly departed folks who, well, really shouldn't be brought back. As we learned from the previous film, the dead don't necessarily enjoy being back, and so "resurrecting" them can create lots of complications. So, this is one of the few examples of love creating negative circumstances.
RON: That's my girlfriend, you numpties!
Ron and Hermione are taking their romance public in this film (finally). When Hermione has a run in with Draco Malfoy's cronies in the Room of Requirement and almost gets killed, Ron doesn't hesitate to come to her defense, chasing the kids off in a full rage.
LILY: Harry, you're so loved. So loved! Harry, Mama loves you. Dadda loves you. Harry, be safe. Be strong.
VOLDEMORT: Avada Kedavra!
This is a flashback to Lily talking to Harry as a baby, right before Voldemort kills her. As we know, her love for Harry managed to protect him when Voldemort tried to "Avada Kedavra" him next.
SNAPE: He doesn't need protection; the Dark Lord has gone.
DUMBLEDORE: The Dark Lord will return. And when he does, the boy will be in terrible danger! He has her eyes. If you truly loved her…
SNAPE: No one can know.
This dialogue is also from Snape's flashback. Snape is grieving Lily's loss, and Dumbledore tries to give him a productive outlet for all those feelings: protecting her son. Snape despised Harry's father, but since he loved Lily so much, he agrees to protect the little boy.
DUMBLEDORE: Lily? After all this time?
In Snape's flashback, Dumbledore has just seen Snape's Patronus, which is a doe. The significance? Well, you know that Patronuses are super personal and used for protection, right? Right. So, Snape's Patronus became the same as Lily's at some point—because he loves her that much. Pretty powerful stuff.
DUMBLEDORE: Do not pity the dead, Harry. Pity the living—and above all, all those who live without love.
We've mentioned that Dumbledore thinks love is pretty much the most important thing in the world, right? It's one of the key things that sets him apart from Voldemort, who has built his whole evil life around avoiding death at any cost (usually by killing others, ironically enough).