Quick Con Law Question

Probably a foolish one, but whatever--and we're on the topic in my Constitutional Law class, so may as well address it now.

The 14th Amendment to the Constitution reads, in part, that "No state shall make or enforce any law which shall abridge the privileges and immunities of citizens of the United States." This clause, as far as I understand it, was meant to overrule the Supreme Court's decision in Barron v. City of Baltimore, 32 U.S. 243 (1833), which held that the bill of rights was inapplicable to the states.

However, prior to the passage of the 14th amendment, the constitution already had similar clause in Article IV, Section II, which states that "The citizens of each State shall be entitled to all Privileges and Immunities of Citizens in the several States." In fact, the framers of the 14th amendment specifically and deliberately used language to mirror the pre-existing constitutional text.

I understand that the 14th amendment's language is slightly more clear and specific than that found in Article IV. But I am curious: what was the purporse or practical effect of the Article IV language originally? Why was it including in the constitution?