According to the bill of rights, what is the reason for not infringing the right to bear arms?

According to the Bill of Rights, the reason given for not infringing the right to bear arms is so that people can form a "well regulated Militia" in order that the United States can remain free. Basically the idea of the militia comes from the time of the British Colonies where individuals were not free to rise up against their government or protect their country from others.