The enemies of the Empire of Man are legion. Pretty much ever corner of the galaxy has something creeping around that wants to undo everything. That could be dangerous aliens. That could be the forces of Chaos. That could just be a disgruntled employee down at the local coffee shop. That means there has to be those that are willing to root out that dissent and get rid of it (usually via bolter). That's where the Imperial Agents come in, their new codex of which for 40k is available to order from Games Workshop.
Along with the codex, there's also a whole ton of Adeptis Sororitas bundles in the webshop. Command squads, assault squads, heavy weapon squads, the Immolator tank, and some command are all available to pick up. The "Nuns with Guns" are coming to make sure you've said your prayers correctly.