This post contains spoilers for Game of Thrones Season 7, episode 4, "The Spoils of War."
On this week's Game of Thrones, Arya Stark finally returned to Winterfell, where she was reunited with her sister, Sansa, and her brother, Bran, AKA the Three-Eyed Raven.
Luckily for everyone involved, Arya's reunion with Bran wasn't nearly as awkward as Sansa's. Instead of alluding to having witnessed some horror of her past ("Hey Arya, I just wanted you to know you looked really pretty the day you went blind"), he gave her a gift. Well, actually it was a re-gift, but still.
First, Littlefinger presented Bran with the Catspaw Dagger—the dagger that was used in the assassination attempt on him in Season 1, because you know, that's a totally appropriate and not traumatizing thing to give a teenager. In one of the most satisfying moments of the episode, Bran responded to the gift by cryptically telling Littlefinger, "Chaos is a ladder," which threw Littlefinger entirely off his game.
Bran, being the Three-Eyed Raven and all, has no use for fancy Valyrian Steel daggers, so he passed it along to Arya, the resident badass in the Stark family (sorry, Jon).
The gift is significant for a couple of reasons. First, the dagger is one of the few known weapons in Westeros made of Valyrian Steel—one of the few substances capable of killing White Walkers. Putting more Valyrian Steel into Stark hands—and especially Stark hands that are skilled at fighting—is always a good thing.
Second, a popular fan theory for the season has Arya adding Littlefinger to her kill list and taking him out. For one thing, the dagger used to belong to him and it would be poetic if it were the weapon used to kill him. Also, Sansa has pointedly said that "no one" can protect her from the dangers she faces. Since one of the biggest of those dangers is Littlefinger and Arya is (or at least was) No One, it only makes sense that she will be the one to save her sister if the time comes.
And then there's Creepy Bran. As the Three-Eyed Raven, he can see everything that has happened ever and even though Littlefinger isn't currently on Arya's list, he's done plenty that would earn him a spot there if she knew about it (betraying Ned, killing Lysa, and, most horrifically, turning Sansa over to Ramsay Bolton for marriage).
If Bran wants to put his newfound powers to use for anything other than the battle against the Night King and making his sisters uncomfortable, he could get Littlefinger in a lot of trouble.