When you bring the container back to Speranzor, he says that it can be opened, but only by using Morgund's key. The key is in the possession of a Grizzly Bear near the entrance to Lost Valhalla.
After collecting Morgund's key and returning to Speranzor, the small container can finally be opened. Inside, Speranzor finds the Frozen Whip and gives it to you, asking that you put it to good use. As you leave, Speranzor requests that you tell Roderic of Rottersvall that he is going to live the rest of his days in Lost Valhalla.