The theme of symbiosis has run through Warehouse 13 for a long time. The relationship between Mrs. Frederic and the Warehouse has been depicted as almost metabolic. But last night's episode took the theme further, showing us how the Warehouse is connected to people two ways: through mystical bonds and through information.
In general, Warehouse 13 often deals with how people are connected to inanimate objects, and how objects become infused with someone's emotions or memories, and thus gain power. But meanwhile, the warehouse, the repository for all these objects, has a mind of its own and is connected to Mrs. Frederic. (Sort of like the Doctor and his TARDIS.) Claudia, as a future Caretaker of the Warehouse, is also connected to it in a similar way. And we glimpse the mystical heart of the Warehouse, where symbols float around in harmony — or not, as the case may be.
And now it turns out that the big villain of the end of the season, Paracelsus, is a former Caretaker — and his bond to the Warehouse challenges Mrs. Frederic. (Sort of how she was in danger when Warehouse 12 was reactivated and there were two warehouses connected to her at once.) Paracelsus is another example of the "crazy evil or dead" rule of thumb for old Warehouse personnel — but it's sort of implied that his hubris in using a mishmash of artifacts to become immortal (and possibly rule the world) comes from being too long connected to the awesome power of the Warehouse. In fact, maybe Paracelsus' hubris is an extension of the Warehouse's.
And then there's information — in this show, information is power, and apparently there's information that even Artie isn't allowed to know, including the details about Paracelsus and why he went bad. Even Mrs. Frederic isn't privy to that — instead there's a whole other person, the Keeper, whose job it is to keep a hold on this information. And it's Abigail, who was undercover in more ways than one as the new Leena, the new therapist and the new Keeper. (Was Leena the Keeper too? I guess we'll never know.)
So it's notable that now, almost every villain the show has given us is either a former Warehouse agent (McPherson, H.G.) a former keeper (Paracelsus) or someone who was affected by the Warehouse (Walter Sikes). This show definitely seems to be exploring the dark side of working in a facility with that much power at your fingertips — even as we see the characters becoming more and more cavalier about using an artifact to solve every possible problem. So maybe it's not symbiosis — maybe it's just an institution that swallows people up and then spits them out, damaged or dependent, somewhere down the line.