Later in the season, Diego finds a file in the Thibodeau’s trash that talks about The Cleanse. In that file, there is a mention of an incident with the Umbrella Academy in 2006, in another timeline, and a mention of October 14 of that year, which is the day that the Jennifer Incident happens. This incident also connects to the origin of The Cleanse.
What The Keepers don’t know is that The Cleanse isn’t going to save them, it could destroy them. As the “doctors” try to get Jennifer back, who ran away after Ben rescues her, Reginald’s wife, Abigailtells them that she is the culprit of the Jennifer Incident and therefore the death of the original Ben and the Cleanse, since, years ago, when Reginald released the Marigold on earth and gave her powers to the Hargreeves, she synthesized the element that created the substance and created a new one she calls Durangowhich, when interacting with Marigold, have a reaction that can destroy worlds.
The Cleanse is a cataclysmic event, a purge, that destroys timelines and everyone in them. This means that everyone in that world will be destroyed if The Cleanse happens and they fail to stop it.
But, The Cleanse It’s not necessarily a bad thing. What happened was that when Reginald released the Marigold and caused the birth of Allison, Klaus, Luther, Diego, Viktor, Ben and Five, the timeline fragmented and with the chaos parallel timelines began to emerge that are now “bleeding” into each other, and that’s why Jean and Gene find artifacts from different realities into theirs. This is why the world keeps destroying itself over and over again and why nothing the Hargreeves do can stop this. Reginald’s wife Abigail is practically the architect of The Cleanse and she did everything to make it happen and to have one original timeline.
It’s all about “cleansing” these parallel lines to try and restore the original. The Marigold also needs to be removed for The Cleanse to work and that means the Hargreeves must sacrifice themselves, combining the Marigold in their bodies with the Durango, so that the purge can work and everything can go back to the way it should be.
