This was a gift from Conicus the night you fled Meadowfen and he was taken prisoner, or killed. Taken prisoner for sure though. He's definitely still alive.
At level 6 it is imbued with a gift from Tyton. It has the same properties as a Pearl of Power. Also, while holding the holy symbol, you can cast the following spells once a day (resetting at dawn).
- Misty Step
- Cat Nap