I recently read a good book on the ratification debates: Pauline Maier's Ratification The People Debate the Constitution, 1787-1788. If you're interested in the debates, check it out. I think people, on average, underestimate how close "we the people" came to rejecting this thing.
I guess I should bust out an employment law tie-in, since this is an employment law blog. The Constitution provides numerous protections for public employees, including due process, equal protection, free speech, free exercise, and more.
For a good example of how the Constitution impacts employment laws in other contexts, check out the Supreme Court's 2012 opinion in Hosanna-Tabor v. EEOC. The Court analyzed some First Amendment issues, including the ministerial exception to federal employment laws.
Finally, what would Constitution day be without the Constitution!? Read it here.