It's also similar to how the pope & bishops refers to themselves during liturgy. All Masses include a prayer for the bishop(s) and pope; when the bishop is the

It's also similar to how the pope & bishops refers to themselves during liturgy. All Masses include a prayer for the bishop(s) and pope; when the bishop is the celebrant, he refers to himself as God's "unworthy servant", and if it's the pope that formula morphs to "your most unworthy servant".