Please, enlighten us.
"A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed."
Basically, it was to prevent militias weapons from being taken away.
Here's a quote from an article that puts in into words better than I'd be able to...
"The purpose of the Second Amendment was to prevent the new Federal Government established in 1789 from disarming the state militias and replacing them with a Federal standing army. It was a concern that was relevant perhaps for a few years around the birth of the country. It is irrelevant today. Americans do not rely on state militias in 2012 for our freedom from the federal government."
So now that we don't rely on militia's anymore, the amendment is completely moot.