Ask Ossian what you need to do to restore the strength of the Lady of the Lake.
Head to the Valley of Saints and fight Barakiel. Kill him, and you will receive the Goddess' Staff.
The staff is only awarded to members of the finishing group who have the corresponding quest.
After receiving the staff, return to Ossian.
THIS QUEST CAN ONLY BE COMPLETED WITH A SUBCLASS.
Starting November 18, an alternative will be available in the form of collecting 3 Shards of the Goddess' Staff. You can collect these shards from the chest after killing Barakiel, starting November 18.