Transubstantiation and Kashrut

The evolutionary debate on http://www.oneambition.com/ got me thinking about Communion. Quite a leap, I know. I'll try and explain if I can.

At one point in college I became very much aware of the mystery of the scriptures. I must have been reading either Madeleine L'Engle (Walking on Water) or Flannery O'Connor (Mystery and Manners) at the time. As a matter of fact, I don't think I was reading either of those authors back then, so actually I don't know where this came from, probably something Wes said once. Anyway, I decided back then that belief in the Catholic doctrine of Transubstatiation had no real bearing on the observation of Holy Communion. God could change the wine into blood if He so chose, and it could still taste just like wine to me. I concluded that it therefore didn't matter whether the description of the elements was either literal or symbolic. I was told by the RUF minister at the time that it really did matter, but I only agreed with about two-thirds of what he ever said anyway, so it didn't bother me much.

I realize now that he may have had a couple of different issues in mind. A) He may have been saying that whether the text was literal or symbolic had some sort of direct bearing on the authority of scripture. Now that I think about it some more, surely not. But the precise nature of the authority of scriptures appears to me to be a major issue in Reformed Theology. (I once laughed at a coffee mug that had something about the complete revealed Word of God printed on it by saying, "Can you fit all of that on a coffee mug?," not realizing at the time that it was a quotation from the Confession.) All sorts of precision appear to be major issues in Reformed Theology. B) I don't remember what the other possibility was. Maybe it will come back to me later.

Back to my point about communion. If at the Last Supper the Disciples all partook of the body and blood of Christ, wasn't kosher law effectively destroyed, in their own bodies at least? Why then did Peter and Paul have an issue about kosher law later? And why didn't Cornelius's vision convince Peter that kashrut no longer had to be observed?

By the way, my dad might be able to answer this one for me: Do Messianic Jews still observe the Levitical Law concerning food?