This quest is the culmination of a couple different quest lines from Witch Doctor Uzer'i. Completion of and the Muisek chain allow you to receive this quest and your choice of one of four rare weapons.
Witch Doctor Uzer'i wants you to wait for a moment while he prepares the weapons.
Imbuing the muisek into the weapons is a difficult process. Now that I have all of the required materials and the muisek of the creatures that you captured, I may begin. Please wait; I will return in a moment.
Did you get it yet?
As promised, you have your choice, <name>. The muisek of the creatures has been forever sealed into the power of these weapons.
You may now wield their energy as your own. Use it well.
-  (The Hinterlands)