Chapter 18 — Part II: The Sacraments — The Holy Eucharist
Section 174. But (between the Eucharist as a Sacrament and a Sacrifice) the difference is very great; for as a Sacrament it is perfected by consecration; as a Sacrifice, all its force consists in its oblation. When, therefore, kept in a pyx, or borne to the sick, it is a Sacrament, not a Sacrifice. As a Sacrament also, it is to them that receive it a source of merit, and brings with it all those advantages which have been already mentioned; but as a Sacrifice, it is not only a source of merit, but also of satisfaction. For as, in His Passion, Christ the Lord merited and satisfied for us; so also those who offer this Sacrifice, by which they communicate with us, merit the fruit of His Passion, and satisfy.