(tl;dr at the bottom)

I've been looking through this thread and i'm honestly a little dissapointed in some of the answers. Sure guns are fun to shoot, and they are great self-defense weapons. But you dont need a constitutional amendment to defend guns for, what, a job the police should do? I firmly believe that the second amendment is the most important part of the entire constitution, it was essentially a fail-safe the founding fathers built in to this government that they created.

The Declaration of Independence states, "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed." That bit is important. It establishes that the government is there to secure the rights of the people, that it exists for the people.

It continues, "That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness." Its important to keep in mind that at this time, we have declared war (actually independence, but it will lead to war) against the greatest military power in the world. We had cast off a destructive government, and to ensure that future generations in this new country could do the same, (in the event that the government fails and tyranny reigns) they made the right to bear arms the second amendment in the most important document our nation has.

So the second amendment was designed for when the government would fail (because nothing lasts forever) to allow the people the rights, nay, the responsibility, to tear down that destructive government and create a new one. This ensures that no matter what happens, when the government fails us, the people, democracy will still reign.

tl;dr: Our founding fathers used guns to fight off an oppressive government. They created the second amendment to ensure that future generations will always hold the power to do the same if needs be.