It captured and focused The Ashen Light of the Great Ashen and allowed the Listeners and Humans to commune with it. When the Great Ashen died, Listener and humanity blamed each other. War raged and Darkness fell, beginning the Third Age.
With the help of the player, Gefn wished to rejoin both hearts using the power at the end of The Gnaw. The player can refuse Gefn and keep the pieces of the heart for themselves.
If given to Gefn, she believes that Amara will know how to find the Ashen.