The Communion Stone is an item which can be bought from Communers in Temples .
Communion Stones are used to set your respawn point at the respective Temple you used it in. It is a one time use item that costs 150 Gold.
Use Communion Stones in cities you will be staying at for a long time or a city where you'll be doing quests in it, or nearby. This is so that when you die, a Boat Ticket will no longer be needed to return to your death point as these tickets are expensive.