It's an old Jewish myth, so it's not something that was invented for the screen. The question is, why put that myth on the screen in Weimar Germany? There's a whole historical thing of Jews being branded as unholy wizards, and Rabbi Loew pretty much is a wizard here, meddling in unholy things. However, he does it to protect his people from the persecution that the film acknowledges was taking place. Moreover, that persecution comes at the hands of the emperor, whose motives are established as unsavory and cruel. And the gentiles at the imperial court are unmistakably horrible human beings, so there isn't a message of superiority in that aspect. But in the end, the message I saw was that the true scandal wasn't that Famulus directed the Golem to murder Florian out of jealousy; it was that Miriam went to bed with Florian, provoking that jealousy. The huge Star of David over the final frames--and over the busted gate of the ghetto--left me with the sense that audiences were meant to be left with the message that the Jewish people would not be contained much longer, and that their big, bad protector would be just as destructive to them, and could be felled by a child.

There's also the matter of the Faustus/Miriam/Florian triangle. The transgression is that the Jewish Miriam and gentile Florian slept together. Faustus sics the Golem on Florian, who kills him brutally. Faustus graciously extends to Miriam his willingness to cover up her sin, agreeing to keep her secret if she submits to be his wife. There is no mention of how he's the one who ordered a hit and has Florian's blood on his hands. What's more is that the film does not avenge Florian. No in-story gentiles seem to even know or care about his death. It certainly isn't the flashpoint for escalating violence. My speculation is that this is because the Weimar audience is expected to feel Florian got what he had coming, for betraying his own kind and sullying himself by sleeping with the Jewish Miriam.