27 It is a good idea to recall at the very outset what may be termed the heart and core of the doctrine, namely that, by means of the Mystery of the Eucharist, the Sacrifice of the Cross which was once carried out on Calvary is re-enacted in wonderful fashion and is constantly recalled, and its salvific power is applied to the forgiving of the sins we commit each day." (12)
Source: Mysterium Fidei (Vatican.va)