I am going to move on to a discussion of Communion. In many ways it will mirror the baptism discussion.
In the spectrum of views on communion we have Roman Catholicism on one end and memorialism (most modern evangelicals) on the other. Catholics believe that the elements actually become that which is signified, while memorialists do not believe that Christ is present in any special way--His presence is no different at the Lord's Supper than it is when we pray or even just think about Him. In memorialism, or Zwinglianism, The Lord’s Supper, like baptism, is not a means of grace but a personal testimony of faith and remembrance.
Luther and Calvin, especially Luther, land mucher closer to the Catholic end of the scale than to the Zwinglian. While they disagreed on the details of Christ's presence, they absolutely agreed that He is present in a way that is very different that, say, during prayer.
Their lack of agreement on the details is understandable. Scripture has left us with a mystery in that regard. However, while the trees may not be discernible, the forest certainly is. The bible is clear that while communion is a memorial of Christ it is also something much more, and His presence is real, and communion and union with Him occur.
This supernatural aspect of Communion is rejected by many because, well it is supernatural. It is as if the creator of all things is incapable of any real presence during the sacrament.
These are just some random initial thoughts which I hope to flesh out in some detail.