Chapter — Wouters, Manual of Moral Theology
Chapter I. On the Obligation by Reason of Order Received
I. Christ imposed upon the college of the Apostles and of priests the precept of celebrating repeatedly. This is of faith from the Council of Trent,1 which declared: "If anyone says that by those words: Do this in commemoration of me, Christ did not institute the Apostles priests, or did not ordain that they and other priests should offer His body and blood, let him be anathema."
II. Individual priests also are bound to celebrate repeatedly, according to canon 805: All priests are bound by the obligation of sacrificing several times a year; but let the bishop or religious superior take care that they do this sacred work at least on each Sunday and on other feasts of precept. It is said several times a year, that is, three or four times per year.
It is disputed whether the obligation of individuals to celebrate repeatedly is of divine law or only ecclesiastical law. Now most authors with St. Thomas (III, q. 82, a. 10) maintain divine law, because a true disorder seems to exist in the fact that one ordained for rendering so great honor to God and for providing so great utility to human beings frustrates such an end (St. Alphonsus, VI, 313; Examen Ordinandorum, n. 111).
III. One who can conveniently celebrate and does not celebrate because of sloth, according to several authors sins lightly, because a venial disorder is had in the fact that one ordained for celebrating neglects so great a good of God and human beings, which he can provide with such ease (St. Alphonsus, VI, 359). For the rest, the same things which commend daily Communion to the faithful persuade priests to daily celebration.