Unlike the priesthood of Aaron in which the high priesthood changed many times because of death of the high priest and unlike the animals sacrificed in the priesthood which should be renewed whenever it was offered for they needed another animal for the sacrifice, the priesthood of Christ was eternal because there is no change in the high priesthood (because the Christ is eternal). Also in this priesthood, there is no need of another sacrifice because Christ completed the sacrifice by offering his body once and for all.