Well... I talked to the overseers and they said we should let them know what we have. So check in with them about it if you haven't already. They were able to tell me the items are "magic," and to hold onto them. And I also talked to someone who's power here is to get more information about an item, and they were able to confirm that they are to be used in a ritual.

However... That doesn't tell us whether it's something the cult need that we're keeping away from them, or if it's something we'll need for our own, different ritual.