Part — Wouters, Manual of Moral Theology
Part II. On the Efficacy, or Productive Power, of the Sacraments
The question is whether the sacraments truly produce grace, etc.; concerning the effects themselves there will be discussion in the following part. Now:
I. The sacraments of the New Law confer grace ex opere operato, or are truly efficient causes of grace. This proposition is established against the Protestants and Modernists, and is of faith from these words of the Council of Trent: "If anyone shall say that grace is not conferred through the sacraments of the New Law themselves ex opere operato ... let him be anathema."1
II. The sacraments concur in producing grace only as instrumental causes; the principal cause, which uses the sacraments as instruments, is God alone; for no creature can, as principal cause, produce an effect which exceeds the order of every creature.2
III. The mode by which the sacraments concur in producing grace is explained in different ways. Some teach that the sacraments, which morally are actions of Christ, move God by an infinite and infallible power to confer grace (the doctrine of moral causality). Others judge that the sacraments do not immediately produce grace, but effect in the subject a title which, so far as lies in itself, demands grace (the doctrine of intentional causality). Others teach that the sacraments physically and immediately produce grace (the doctrine of physical causality). This is the opinion of St. Thomas (I-II, q. 112, a. 1, ad 2; III, q. 62, a. 1, 3, 4, 6).