QUERY: If the Magisterium of the Church is infallible, why do Catholics have a Bible at all? Why shouldn't they just be rid of it? What good is it to them? Can't they know everything through Tradition? It would seem there is no real role for the Bible at all, but we know the Bible is important, therefore the Magisterium must not be infallible, which means Protestantism is (at it's core) right.
This argument has a hidden premise, which is the causing confusion and leading to a fallacious conclusion. The argument is assuming the Protestant view of the Bible, that the Bible exists to be a regula fidei,
a rule of faith. Again, this argument assumes, doesn't prove, that this is true and then asks, if
the Church is the pillar of truth why do we need the Bible (another
pillar of truth).
But this view of the Bible is exactly what Catholics and Protestants differ on. The Church doesn't understand the Bible to be a rule of faith nor does the
Church see the Bible as being opposed to Tradition. The Bible is
simply the written portion of Tradition. The role of the Church is akin
to that of the Supreme Court, it interprets Sacred Tradition - both
oral and written (i.e. the Bible). Just as it is supremely absurd (bad
pun, I know) to claim that the existence of a written Constitution makes the
organ that interprets it (the Supreme Court) redundant, so to it is
absurd to claim that the written portion of Sacred Tradition makes the
interpreter of Tradition redundant or for that matter that the interpreter makes the Constitution redundant!
Protestants are to be loudly commended for loving, reading, and studying
the Bible. Unfortunately, because of the bad theology of their distant
fore-bearers, they try to make the Bible do the job Christ assigned to
the Church, i.e. being the pillar the truth (cf. 1 Tim 3:15)