Section — Noldin, Summa of Moral Theology
Section 2. On the Attention of the Minister
19. On due attention. Attention is an act of the intellect, namely the application of the mind to those things which are being done. One is internal, which is defined as the very advertence of the mind to that which is being done; the other is external, which consists in the absence of any external action which cannot coexist with internal attention. Therefore external attention requires nothing else than that the external rite be performed in a human manner, that is, in such a way that the minister knows what he is doing.
a. For the valid administration of the sacraments external attention is required and suffices: for that attention is required and suffices by which the administration becomes a truly human act; but for this external attention suffices. Therefore even a distracted minister, and one thinking at the same time about other things, validly confers the sacraments.
b. But for the licit administration of the sacraments that internal attention is required which excludes every voluntary distraction: for the reverence due to the sacraments and the obligation of avoiding the danger of error in the conferral of the sacraments demand internal attention also.
Voluntary distraction in the administration of the sacraments does not exceed venial fault, unless the minister exposes himself to the danger of erring in those things which pertain to the essence, and therefore of frustrating the sacrament. According to certain authors, because of the dignity of so great a sacrament, voluntary distraction in the confection of the eucharist is a grave sin; yet several authors contradict this opinion, which therefore cannot be called certain.1
1 Cf. Lacroix, bk. 6, pr. 2, n. 443.