ex opere operato
It seems wrongheaded to me to frame the Protestant objection to the Roman Catholic sacramental teaching of
ex opere operato in terms of sacramental "efficacy." As Turretin remarks, "the question here is not 'are sacraments efficacious?' since this is granted on both sides. The question is
how they exert their efficacy" (
Institutes, 8.19.6)
Indeed, one might argue that classical Protestant theology ultimately sees the sacraments as having
greater efficacy than traditional Catholic teaching did.
Now, we should recall that the Catholic church teaches that "to attribute the efficacy of prayers or of sacramental signs to their mere external performance, apart from the interior dispositions that they demand, is to fall into superstition" and is a violation of the First Commandment (
Catechism 2111). While this emphasis in the current Catechism may have been muted in, for instance, certain kinds of late medieval theology, it has always had some role in Catholic teaching.
But there's the rub. "Interior dispositions" is a wide-ranging concept, including, depending on circumstances, not only faith, but also perfect contrition, freedom from all unconfessed mortal sin, right intention, proper devotion, and so on. From a Protestant perspecitve, faith appears here to be mixed together with various other spiritual works, distinguished from faith itself and added to it (almost extrinsically on some of late nominalist construals that the Reformers were resisting).
The Protestant view is that in the Word of promise enacted in the sacraments, God offers Christ to us and he is received therein by faith alone through the Spirit. While faith certainly may be accompanied by and produce various other effects in the recipient, it is faith which alone receives Christ in the sacraments, even if the sacraments themselves are a means by which faith is quickened and increased.
Moreover, taking the particular case of the sacrament of baptism, while the Catholic church does teach that "Baptism is the source of that new life in Christ from which the entire Christian life springs forth" (Catechism 1254), baptism itself is limited in its effects so that sacramental reconciliation functions as a sacramental necessity
in addition to baptism when new (mortal) sins destroy the sacramental grace that had once rendered the sinner righteous (which, it would seem, is part and parcel of a more transformative understanding of justification over against a Protestant understanding of imputation).
The Protestant view, however, is that baptism is effective not only when the water is upon us, but for our whole lives (see Calvin,
Institutes 4.15.3;
Belgic Confession, Article 25; Turretin,
Institutes 19.19.12-23). Subsequent sin and confession receives forgiveness as a way of living out and improving our baptisms, so that the very same justifying verdict received in baptism is received anew as part of an ongoing status before the face of God.
Thus, on these two counts, at least, the Protestant view of the sacraments holds that sacraments, as covenant signs and promises by which Christ is offered to us in the Spirit, are
more efficacious than in certain kinds of Roman Catholic views, requiring less of the recipient and having a greater effect.
If so, then the Protestant objection to
ex opere operato, as Turretin commented, cannot be aimed so much at the notion of efficacy per se, but at the notion that sacraments somehow "contain" the grace they signify, particularly as that is understood in an almost physicalist manner in some sorts of late medieval thought.