...is to balance against human weakness.
Imagine if America's founding fathers had
written the Constitution and allowed every American to interpret it
individually. Who can argue that the Supreme Court is necessary to be
the final word on what is and is not constitutional?
Even the ancient Jews who had the Torah didn't use it alone. They
used their scriptures and their tradition in union to ensure no one
incorrectly interpreted Scripture and no one created tradition opposed
to the Torah.
Catholics do the same thing by relying on the
Bible but protect against false interpretations by remembering what the
earliest Christians believed (tradition) and by reserving binding
decisions to a particular group (called the Magisterium or “teaching
office”). These three entities balance and protect each other from our
human desire for seeking our own advantage.
While the Holy
Spirit is responsible for interpreting Scripture for us, our fallen
nature still can get in the way. Without tradition or the Magisterium
then who makes decisions on what Scripture means? I do. What happens
when you and I disagree? We go and form our own churches.
This is yet another reason why Catholics don't rely on the bible alone.