Some say this movie was rushed, but...

I think the director did really well with the 1.5 hours he was given, although I completely agree that the Scott Glenn character had no arc or depth. That's a bummer.

It seems like Rasalom is supposed to symbolize vindictive aggression. The Jewish man (I forget his name), saw an opportunity to grab power over the Nazis after having endured the infamous oppression of his people. Rasalom manipulates the man by pretending to empathize (that scene where he yells about "MY PEOPLE!??" and vows to "destroy" the group killing said people). Also, the empowerment of his newfound aggression makes him feel (look) youthful.

But, Scott Glenn (whose green color scheme is at obvious contrast with Rasalom's red scheme) warns that the manipulated man should not bring some kind of talisman out of the keep. This would let Rasalom out into the world, and global destruction would ensue. There's not much evidence that this would actually happen, except that Rasalom urges the man to kill his daughter for standing in his way at the end. A force that urges such an act surely wouldn't be a healthy influence on humanity.

Carrying the talisman out of the keep would symbolize spreading his newfound vindictive aggression beyond that isolated incident. In that incident, it would help him escape his captors. Spread to the rest of the wronged population, it would be destructive, and would have led his people to more closely resemble their Nazi tormentors. So, the story warns us against fighting evil with more evil.

That said, I think he and his writers included just enough detail to convey that message.