The chief issue that has caused me to shift my theological and ecclesiological identity from Baptist to classical Protestantism of the Reformed and Presbyterian strain is the nature of baptism and the Lord's Supper. For me, I have become convinced that we should understand these rituals related to Christ's redeeming death and resurrection primarily in terms of God's work of using tangible signs and symbols to apply his promises of salvation to us. In other words, baptism and the Lord's Supper are sacraments. This is quite different from the Baptist and mainstream evangelical view that they are primarily memorials and human actions of obedience to attest faith in Christ, and thus that God is not at work in them in a particularly special way (at least not in any way that has to do with "things" or an objective Divine action for the church or for the members-God may very well be working subjectively in individuals' hearts or even in a way that engages the community but quite regardless of the "stuff" involved). For simplicity, I will describe this as the commemorative ordinances view.
Keep in mind, this distinction between sacraments and ordinances is a bit simplistic. They aren't polar opposites. We should understand this as more of a continuum than as an either/or proposition. That being said, we can most certainly sketch a theological divide between the view of baptism and the Lord's Supper as sacraments and the view of them as ordinances. I would submit that this issue is more broadly significant than the narrow question of what “happens” in these rites. The distinction reveals in the theologies of which each view is part important differences in hermeneutics and in understandings of the scope and nature of salvation, the ways in which God applies that salvation, the ways in which God is more broadly at work in the world, and somewhat different views of what constitutes faith.
The differences are not irreconcilable and I'm quite confident that most holders of both the sacraments' view and ordinances’ view are solidly orthodox Christians, but the differences of understanding in the bigger issues at play in this question were significant enough to compel me to shift my identity from a Baptist to a protesting catholic of a confessionally Reformed stripe. Furthermore, the issues involved in this question have been significant enough to constitute the biggest fissure dividing Protestants historically. It is this issue and not the sovereignty-free will debate that is the most fundamental divide between Christians this side of the Tiber (though it is quite likely they are connected somehow).
The following are the points at which I believe Christians who think otherwise can learn and benefit from the commemorative ordinances view of the sacraments.
1. This view is part and parcel of that common sense that makes the Baptist form of Christianity that most quintessential American Christianity. The faith that God is not bothered or hindered by nonexistent ecclesiastical structures or Christian social structures in non-Christian lands and on the American frontier—the faith that God can and does save even if there isn't anybody around to baptize you—was a huge factor in the evangelization of the North American continent and the Modern Missionary Movement.
2. This viewpoint is not susceptible to the obsessive, myopic focus on the bread and wine that has characterized Eucharistic theology for 2000 years. Obviously, what's going on with the symbols of Christ's body and blood is vastly important, but there are other considerations in play at the Lord's Table than how exactly Jesus is present in or with the elements.
3. In connection with the above point, the commemorative ordinances view of the sacraments is not susceptible to the blasphemous and objectifying instinct humans have to try to know and explain in precise, scientific detail the mysterious workings of God. If holders of the commemorative ordinances view shortchange themselves by failing to see God's special action through water and bread and wine, they do not shortchange themselves by killing the thing with scientific, metaphysical terminology and scholastic theology! No bothering about with "accidents," "pneumatic presence," "transubstantiation," "sacramental union," or thinking about "grace" as some kind of gas, substance, or goo to be accumulated.
4. Again, in connection with the previous points, if the sacraments are about communing with Jesus and seeing him face to face (in your fellow Christians' faces), trying to figure out how it's all working or thinking in terms of getting ready to receive something, i.e. "grace," rather than Someone seems to get in the way of experiencing Jesus. Holders of the commemorative ordinances view are not thinking about receiving a gift abstracted from the person of Jesus but rather about God's great gift of the Giver Himself, Jesus Christ. There's nothing to distract from Jesus when there's nothing but Jesus, even if it is just "Jesus in the air."
Next time, I will address the big points where the commemorative ordinances view fails to capture adequately the full and glorious biblical teaching about baptism and the Lord's Supper.