Thanks! One of the coolest theories was that Arya might have taken Jamie’s face in order to kill Cersei. That would have been absolutely amazing, but her journey ended with saving the world from the Night King. Everything after that is using her as a witness for the final acts of the show.
The rule of three is a key principle to good graphic design (my actual profession), and writing (my favorite hobby).
Arya is one of the key witnesses over the course of the last two episodes.
In Episode 5, we see the see the horror and devastation of the now (choose one) Mad-Traumatized-Power-Corrupted Dragon Queen from the perspective of Jon (who tries to stop the slaughter of men who surrendered, and then kills a Northman trying to rape a woman), the Hound (as he battles the Mountain), and Arya, as she runs through King’s Landing trying to save others, but ultimately failing as everyone gets incinerated.
In Episode 6, we see the rule of three in the call to the reluctant hero, Jon. First, he see Grey Worm committing war crimes by murdering prisoners under the orders of the Queen. Next, he sees Arya after Daenerys’ liberate the world through fire and blood speech. She tells him that Sansa will not bend the knee, that he is not safe because of his true identity, and that she knows a killer when she sees one. Tyrion will tell Jon the same things in reverse order, ending with the statement that Jon’s sisters will not be safe.
It is only after those three events that Jon meets Danerys and does a subtle verbal dance with her, and touches each of the three ideas presented by Arya and then Tyrion. When Jon gets to the question of what if other (Arya and Sansa) people have their own idea about what is good and right, Daenerys responds “they don’t have a choice.” Jon gets his final confirmation that his sisters can not survive in a world with this tyrant, then professes his loyalty and love for Daenerys, kissing her and plunging the knife in her heart.
It’s beautiful Shakespearean tragedy. And that’s why millions of people were so moved by the show.