"Jesus Christ, whose body and blood are truly contained in the sacrament of the altar under the forms of bread and wine; the bread being changed (transsubstantiatio) by divine power into the body, and the wine into the blood, so that to realize the mystery of unity we may receive of Him what He has received of us. And this sacrament no one can effect except the priest who has been duly ordained in accordance with the keys of the Church, which Jesus Christ Himself gave to the Apostles and their successors."