Holy Orders and Matrimony are called sacraments in service of the community because they confer a specific mission on their recipients to build up the people of God. Christ instituted Holy Orders at the Last Supper by conferring on the Apostles the power to consecrate and offer his Body and Blood in the Mass. The chief supernatural powers of a priest are to change bread and wine into the Body and Blood of Christ in the Mass, and to forgive sins in the sacrament of Penance.