 Similarly, if Mary is described as the "mediatrix" of all graces, it “is to be so understood that it neither takes away from nor adds anything to the dignity and efficaciousness of Christ the one Mediator”.Pope Pius XII in "Munificentissimus Deus", the bull defining the dogma of the Assumption of Mary, used the expression "the revered Mother of God, ... joined ... with Jesus Christ in one and the same decree of predestination ... as the noble associate of the divine Redeemer".This whole topic is made more complex by the evolving understanding of what "sacrifice" means in the Catholic church, whether it is propitiatory or expiatory.