Jowdy inhabits Sarah. BOB built the box to bring Jowdy out. BOB raised a ruckus enough for the Lodge to release Coop (a trick by BOB) and open a flow out for Jowdy who followed Coop. But Diane sacrificed to break the jail cells and let Coop go. Jowdy followed and inhabited Sarah, hoping BOB could figure it out . But BOB didn't (who is Judy? Means who is Jowdy inhabiting)
BOB wanted to bring her into this world and get back with Jowdy.
The White Lodge fought this from the time that the nuke opened earth up to evil. They gave Laura-essence down as a destructive agent of purity into the bug that inhabited Sarah (her child to be with Leland that 'should' have been for Jowdy). BOB inhabited Leland and spent years trying to destroy/prepare that child. The black lodge always wanting to bring Jowdy across somehow. But the giant put the weapon (Laura purity essence) into the vessel. Then when Laura (the poor person) could take it no more, the one armed man gave her the ring. The ring pulls the wearer's essence back into the lodge and so denies their possession. Laura was free, though the weapon was trapped.
Then good Coop wanted to alter that past and, fearing that the Laura weapon would be free, Jowdy pulled her away and dropped her in the new timeline as Carrie. That's why those scenes screams were the same. They both occurred synchronically.
Badcoop was trying to find Jowdy, but failing to put dirt in his pocket, he was shifted from his intentional location of the Palmer House to jail and then shifted to the Sherrifs Dept where the trap was laid by the White Lodge pre-arranging things and bye BOB.
Coop goes to save Laura in the past, but Jowdy pulls her out (of the lodge in front of Cooper and from the woods in Coopers hand). Cooper decides to jump into that time with Diane (because he loves her too much to lose her). Sadly, Diane/Linda is unable to transition in her mind and becomes Linda. Cooper stays Cooper which drives off Linda (who can't understand why Richard changed so much) and Linda leaves.
Cooper is realizing what a lonely quest he is on. He's giving up all. He is a little darker for that.
He follows his instincts and finds Laura/Carrie. He takes her to the Palmer House to confront the inner Sarah with the inner Laura. But he is too late. Years have passed. How many? Sarah has moved.
Meanwhile Carrie starts to realize all the sheer horror she's been forced to endure in her unwilling role as 'weapon against evil that came to earth during nuke'. It all clicks and she screams.
The weapon is back and Coop realizes he just might be chasing Jowdy through an infinite loop or, at least, several years after 2015. (If Lynch builds in a season four)
But it could be infinity. (like Sarah's television - and being disturbed by the change in jerky that threw her off, as Jowdy obviously has trouble with linear time). As Jeffries 'said': 8. The infinity symbol of loops.
Cooper will (perhaps) endlessly threaten evil, gathering, protecting and delivering Laura.
That last 'infinite' part is a guess though. Cooper messed with time.
This is very similar to what I starting to piece together (see the thread, "Wait a second, was this actually a happy ending?"). Although my guesswork had a slightly more optimistic spin wherein Laura's scream at the end might have actually vanquished/banished Jowday, who was "in our house," right then and there, signified by the crackle of electricity and all of the lights going out. Definitely a counterintuitive read given all of the horrifying and dark visual and aural cues leading up to that scene, and the reprise of Coop's shocked/confused expression while Laura is whispering to him during the end credits, but feels like a fitting flip-side to the Lynchian theme of dark/awful things lurking below the surface of what appears to be contented and serene.
Fire walk with