The Altar of Weor grants the increase in the Gold and Iron production rate by 5% with each upgrade level.
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 in your castle the garrison capable of defending it and annihilating any hostile army which encroaches on your resources.