Thanks for pointing this out, Bryan (nice name by the way). This is an excellent point, and I may add another blog post including this information. There is just so much more to be said about this issue, so I'm not sure how much longer I will keep treating it in the blog.

Marie, I should have mentioned that the interpretation you are offering is one that Augustine held. Actually, he had taught that the Rock was Peter, but later in life he changed his position and taught that the Rock (in this passage) was indeed Christ.