Melissa, I recall that you expressed basically the same concern in another recent thread ("Baptism Flip/Flop"), and Fred Greco gave a brief reply and pointed you to some former threads in which he had explained the issue more in-depth. Did you read those threads? If not, I would highly advise you to read them, as I too have struggled with the concerns you are mentioning, but I understood the biblical wisdom in confessionalism much better after reading Fred's treatment of the issue in those threads. In case you haven't read them, for convenience's sake here are the links:
http://www.puritanboard.com/forum/vi...d.php?tid=1710
and,
http://www.puritanboard.com/forum/vi...d.php?tid=1227
He also pointed out in that recent thread the same thing I just now mentioned, which is that Mormons' and Catholics' confessions are set in stone, whereas Westminster's is amendable if part of it can be found to be contrary to Scripture. A confession that is amendable as such yet which is expected to be adhered to is exactly the thing needed to produce a church that is ultimately answerable to Sola Scriptura and yet is unified and enduring at the same time, not ending up in a split 10 years after its formation because of theological liberalism and disagreement.
Hope this helps,