Ask Ossian what you need to do to restore the strength of the Lady of the Lake.

Recover the Ring of Goddess: Waterbinder and Necklace of Goddess: Evergreen. The ring can be obtained from a Pilgrim of Splendor and the necklace can be obtained from a Judge of Splendor.

Monsters to Hunt - Pilgrims of Splendor and Judges of Splendor

You've recovered the Ring of Goddess: Waterbinder and the Necklace of Goddess: Evergreen. Take them to Ossian in the Town of Goddard.

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.

Take Rain Song, the Staff of the Goddess, to Ossian in the Town of Goddard.

Deliver the three sacred relics of the goddess to Magister Ladd at the Ivory Tower. He's discovered a way to tap the sacred power contained within them.