The Altar of Weor grants an increase in the Gold and Iron production rate by 5% with each upgrade level.
The Altar of Weor does not have any defensive capacity and will be destroyed if an enemy successfully assaults your castle and, therefore, returns to Level 1. You then need to upgrade it again.
To prevent its destruction, keep the Castle garrison capable of defending it and annihilating any hostile army that encroaches on your resources.