Specifically, it matters that Adam was a genuinely historical figure.
On Sunday I preached a message dealing with Genesis chapters two and three. One of the things that becomes quite clear is that Adam and the fall are, indeed must be historical realities. This is confirmed by Paul in Romans five. If Adam and the fall are mere metaphors then the gospel itself must be reformulated.
Little wonder then why liberal Bible scholars and emergent's like Brian McLaren who deny the historicity of the fall also diminish Christ and His cross. They deny the atonement because if there was no fall then there need be no sacrifice for sins.
H. Richard Niebuhr's summation of liberal protestantism still rings true:
"A God without wrath brought men without sin into a kingdom without judgment through the ministrations of a Christ without a cross."
Check out this helpful article on the importance of Adam to Paul's epistle to the Romans.