In the glossary it says:
ABILITY (B4) - A special rule listed on a card is effective as long as the card is unsilenced and in a tableau. Ability effects are cumulative.
Therefore, I say that this ability can be silenced by a bishop.
In most Pax games, a "golden rule" is included that states that rules on cards supersede rules in the book. However, Pax Renaissance does not have such a rule, because I am attempting to make the game work without recourse to such a hierarchy. I may come to regret this.
So what happens when there are two or more such cards in tableaux? Would they protect each other?
I have Humanism and Hermetism in my tableaux.
My opponent places bishop on Humanism. But it is not silenced because Hermetism ability protects it. So I have two active protection abilities. If opponent now moves second bishop on Hermetism, there are two separate protection abilities- so they are both active, or both inactive after the move.