Game of Thrones: Season 7, episode 5: What is the significance of the scroll which Littlefinger hid and which Arya found?

Littlefinger is, basically, what my mother used to call a shit-distributor.

Littlefinger's goal, of course,  is to drive a wedge between Sansa and her siblings; and then use that distrust to manipulate Sansa into staging a coup and taking over Winterfell.

(For the record, if you didn't pause the play on your illegally downloaded episode of Eastwatch, like I did you might have missed the fact that the scroll which the maester brought Littlefinger was the letter that Sansa wrote in Season 1 under Cersei's orders, asking Robb to bend the knee and submit to the Lannisters because Ned Stark was a traitor. )

Now, We have already seen tension between her and Jon.

But there are some details that are easy to miss in episode 5 that give clues as to what is really going on.

Here is what happened:

1. Sansa holds a large — and blessedly Lyanna Mormont-free — council. Many of her lords seem very unhappy with Jon’s absence. Glover and Bronze Yohn Royce are particularly vociferous in their objections. Glover flat out states: We did not choose you(Sansa); but perhaps we should have. Royce says: The Knights of the Vale came here for you, Lady Stark.
2. Lady Stark stays the course.
3. Later Arya confronts Sansa and accuses of her trying to usurp Jon’s chair. Arya is QUITE unreasonable; Sansa is very smart and political.
4. Arya sees Littlefinger collecting information from a serving wench; and consulting with Royce and Glover.
5. Littlefinger sees Arya spying on him but pretends not too.
6. Littlefinger gets the raven-scroll and hides it, knowing that Arya is watching him and will go into his chamber and find it, thus cementing her distrust of Sansa..

Now he thinks that Arya is going to move against Sansa; and that he can manipulate Sansa into getting rid of Arya: who is a scary badass assassin, utterly loyal to Jon. And who already just naturally doesn’t get along with Sansa; and who Sansa is kind of freaked out by.

It was by far the most interesting set of scenes in the episode if you ask me.

Of course his plan will backfire. Either Arya (and possibly Sansa) are already on to him or will be soon; or because Bran will see what’s happening and do something useful instead of just seeing the Army of the Dead coming, which everybody already knows, and tell them.

Then Littlefinger will be, in the words of Davos, “fooked.”