“In which the story is finally ready to get started.”
Frankly, this should have been the first episode of the season. That's not to say that the events of the previous three episodes weren't important—there were absolutely loose ends that needed to be tied up—but that they could have been told via a five-minute narrated montage and little would have been lost.
With this episode, the stakes are finally out in the open. Clayman has sent a spy into Tempest, and the Kingdom of Falmuth is planning to march to war against a yet-unaware Rimuru. Worse yet, the war will likely be branded as a holy war, forcing other nations into the fight and all but assuring genocide for the monsters of Tempest should they lose.