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 Roman 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.

Having said all of that, what exactly is wrong with saying that baptism or the eucharist works ex opere operato?

That's not a bad question since most Christians, traditional Protestants included, maintain that in baptism God does something and what God does in and through the sacrament is something objective and effectual. As the Anglican 39 Articles say, sacraments are "certain sure witnesses and effectual signs of grace and God's good will towards us by which He doth work invisibly in us, and doth not only quicken but strengthen and confirm our faith in Him" (Article 25). Or as the Westminster Standards maintain, sacraments are "effectual means of salvation."

So, then, why do Protestants generally object to the phrase "ex opere operato"--that what is accomplished through the sacrament is accomplished in the doing of the sacrament?

There are several reasons, the primary one being historical, given what the phrase had come to mean for many (nominalist) theologians at the time of the Reformation (that the sacraments work "automatically") and given the dominance of certain (quasi-Thomistic) ways of understanding sacramental causality (that the material element of the sacrament is itself a "cause" of grace). Moreover, the Protestant Reformers understood the notions of sin and grace rather differently from many of their Roman Catholic counterparts and thus in rejecting ex opere operato, they were rejecting a particular notion of what it might mean for a sacrament to "cause" or "confer grace" and the kinds of effects that such words might envision.

Still, to be entirely fair, the phrase "ex opere operato" does need to be understood in its larger context.

First, the term itself seems to be first used by Peter of Poitiers in around 1205 and then was picked up by subsequent theologians like Thomas Aquinas and pope Innocent III.

Second, it should be noted that the term "ex opere operato" originally arose in the context of and as an affirmation of the validity of heretical and schismatic baptisms. It was intended as an affirmation of their validity despite the questionable sanctity or orthodoxy of the minister. It was not intended as a theory of how "grace is caused." It only came to take on that further meaning later.

Third, only in the context of late medieval nominalist theology did "ex opere operato" come to mean that grace was conferred "automatically" or "magically" (due in part to the ways in which nominalism had shattered the philosophical underpinnings of earlier medieval theology). The emergence of this "automatic" view of the sacraments and its growing influence on popular piety was the immediate context of the Reformers. Thus, in their eyes, "ex opere operato" came be to regarded as a serious error since, for them, rightly or wrongly, it was synonymous with the sacramental abuses they were presently facing.

Fourth, dogmatically, the precise phrase is not often used in the official teaching of the Roman Catholic church. Rather one primarily finds things like Canon 6 of the Council of Trent's Decree on the Sacraments, which condemns the teaching "that sacraments of the new law do not contain the grace which the signify, or that they do not confer this grace to those who present no obstacle." Canon 8 of the same decree does go on to use the phrase "ex opere operato", but only to oppose those who maintain that faith receives grace only apart from any sacramental means, a view that was not in the mainstream among Protestants.

Thus, it seems that there are three fundamental teachings that are dogmatically defined by the Roman Catholic church with regard to sacramental causality:

Thomas Aquinas and the Dominicans taught that the rite itself was an "efficient instrument" used by God to produce grace, where God in Christ by the Spirit is the cause of grace but such grace is effectively received through the sacrament as an instrument.

One group of Franciscans, following Bonaventure, considered the rite and other human actions as "moral causes" of grace just a prayer can be considered the cause of its being answered since God freely choses to answer it.

Other Franciscans, following Duns Scotus and others, saw the sacramental rite as having an "occasional causality" so that the rite causes grace not because of anything done by those who perform or receive it, but because God has made a solemn promise (pactum) to give grace on those occasions when Christians do particular actions. (It is within this kind of theology in its later developments, by the way, that theologians such as Gabriel Biel emerged; this theology also equally serves as the medieval predecessor for Reformed covenant theology).

Jesuits and other later theologians offered various other theories and revisions of earlier theories. All of these different theories were represented at Trent and the Council's decree on the sacraments was not intended to chose among them or settle the matter entirely.

Today many Catholic theologians focus upon the communal and symbolic context of the sacrament as central to sacramental causality, as well as the way in which Christ did not merely institute the sacraments extrinsically and explicitly, but embodied them in his own person and work. This comes out in the focus of the Second Vatican Council upon the Church itself as the "basic sacrament" of Christ's action in the world by the Spirit. It also comes out in the Council's focus upon the centrality of Christ and the paschal mystery--what Jesus accomplished once and for all in the cross and resurrection and what he continues to actively do within his Church on the basis of that prior accomplishment. Notions of sacramental causality, therefore, have to be appropriately adjusted to the ways in which theology has continued to develop.

With this background and history, I think Protestants could admit that what "ex opere operato" was originally intended to express is perfectly consonant with Protestant doctrine. After all, we are not Donatists. We may well also find some sorts of medieval notions about sacramental causality to be compatible with Protestant understandings of sin and grace, not to mention how those categories have been further repristinated and developed by more contemporary figures such as Rahner and de Lubac. One could make a case, then, even from within mainstream Protestant theologies, that the phrase "ex opere operato" is a perfectly appropriate and meaningful description of God's work through the sacraments, at least if that is rightly understood.

But I think it is also important for Roman Catholics and those of us Protestants who have a stronger sacramental emphasis to realize the theological context in which Protestantism came to understand and then reject the notion of ex opere operato (and I am reminding myself of this here as well). When most Protestants hear the phrase, they hear it with a historical understanding that is thoroughly shaped by the theological currents of the late 15th and early 16th centuries. Prior and later developments are not part of the equation and there is little popular understanding of the theological variety that was present within medieval theology. Thus the phrase is quite misleading to the typical Protestant ear and, in most contexts, probably should be avoided.

Still, one might suggest that there are ecumenical reasons why, within a limited context and with proper qualifications, it could be used in order to build bridges with those brothers and sisters from whom we still remain separated. At the very least, understood rightly the terminology, in and of itself, may not necessarily be a barrier to ecumenical convergence.