Early on in the production of WandaVision, it became apparent that the show would introduce S.W.O.R.D. -- Sentient World Observation and Response Department -- to the Marvel Cinematic Universe. Early set photos showed Teyonah Parris playing Monica Rambeau entering an office building with the S.W.O.R.D. logo on the glass door. However, no official confirmation existed until the most recent trailer for WandaVision, where a "beekeeper" was seen emerging from a sewer with that same logo on his back.
Evidently, S.W.O.R.D. will be playing a crucial role in the new Disney+ MCU series. While it remains to be seen why S.W.O.R.D. has any interest in Wanda Maximoff's hijinks, there are a few possible reasons as to why the organization is involving itself in the events of WandaVision.
WHAT IS S.W.O.R.D.?
Serving as the first line of defense between the world and space, S.W.O.R.D. serves to protect Earth from any and all alien threats that could put the planet at risk. Its located in a space station known as the Peak, which floats over the planet, and its leader, Abigail Brand, is a ruthless mutant who will do her job without question.
S.W.O.R.D. has several ties to the X-Men, as it first appeared during Joss Wheadon's run on Astonishing X-Men. It was one of the first organizations that the Skrulls took out during the Secret Invasion event, was manipulated by Norman Osborn's H.A.M.M.E.R. during the events of Dark Reign and more recently, returned in its own series as part of the Reign of X event. S.W.O.R.D. is also responsible for Alpha Flight taking on a role as defenders of the cosmos.
S.W.O.R.D. IN THE MCU
One vital component when considering how S.W.O.R.D. fits into the MCU and WandaVision is to understand that the organization is different than anything fans have seen in the franchise. While S.W.O.R.D. started as a subdivision to S.H.I.E.L.D., as time passed, the two became further divided. Captain America: The Winter Soldier saw S.H.I.E.L.D. collapse and Agents of S.H.I.E.L.D. saw the organization gradually rebuild itself, but there's a solid chance that S.W.O.R.D. was barely affected by any of this.
It's possible that S.W.O.R.D. might've been started in the MCU following the events of Captain Marvel, thanks to the Skrull invasion, or after The Avengers, following the Chitauri invasion. If that's the case, it would have been founded in order to defend the Earth from the extraterrestrial forces that Nick Fury confronted, something that the spy was clearly focused on in the post-credits scene of Spider-Man: Far From Home.
S.W.O.R.D. IN WANDAVISION
Still, while these ties to the greater MCU are interesting, it doesn't explain why S.W.O.R.D. is in WandaVision. After all, it seems as though Wanda is the catalyst of why everything is happening in the series, and if that's the case, then it makes little sense why S.W.O.R.D., an organization that deals with extraterrestrial problems, would be concerned with a very terrestrial incident.
One might argue that, because WandaVision deals with a universe-warping or extra-dimensional threat that this falls under S.W.O.R.D.'s jurisdiction, but, again that doesn't mesh with what has been revealed so far. Fury -- or, rather, Talos pretending to be Nick Fury -- dealt with the perceived multiverse threat of the Elementals in Spider-Man: Far From Home. If S.W.O.R.D. dealt with threats from other universes, Mysterio would've been working with Abigail Brand, not Fury.
Of course, one possible explanation is that the source of Wanda's power, the Mind Stone, is an object that comes from beyond Earth. It might be that, following the Snap, that all new matters involving the Infinity Stones fall under S.W.O.R.D.'s authority. However, all this assumes that Wanda is the only factor at play during the events of WandaVision. It remains to be seen if there is an extraterrestrial threat involved, manipulating Wanda's wishes to enhance her abilities.
Another possibility is that S.W.O.R.D. is involved because they don't know what's going on. The organization might suspect it's an alien, especially following Thanos's actions, but, as time goes on, realize the threat is far more down-to-earth, much like how Talos and the remnants of S.H.I.E.L.D. didn't realize what the Elementals were until the end of Spider-Man: Far From Home.