The republican theorist and political strategist Niccolo Machiavelli wrote in his Discourses that “a good militia is the foundation of all States, and where that is wanting there can neither be good laws, nor aught else that is good.”
Couple Machiavelli’s position on militia, as the foundation of good law, with the perennial dictum of Chinese communist revolutionary, Mao Tse Tung, that “political power grows from the barrel of a gun” and you can understand why the US Constitution diffuses law enforcement power to the militia as critical civic self-government institutions.
The militia are necessary to the security of a free state because they place the people into the final, and most crucial step, in a circuit of self-governance.
As the executors of law at the local level, the people themselves understand conditions in their communities and how to apply legislation to best suit their needs in consonance with the needs of their neighbors. Further, and more importantly, the people themselves serve as a check on the types of legislation that get carried into execution.
The militia system builds the consent of the governed into Constitutional practice. With the people, as militia, carrying law into execution at the local level they reserve the right to nullify unlawful legislation. The laws that local militia execute must be clear, make sense, apply to their circumstances, and conform to the delegated authorities granted to the respective general or state governments.
To have the people directly involved in the execution of law is The Way of maintaining a well-functioning federated republic that serves the purposes for which it was formed. To establish justice, secure liberty, and promote domestic tranquility requires keeping each branch, office, and level of government constrained to the limits of their delegated authority.
The real purpose of the Second Amendment is to chasten the inclination toward tyranny inherent to political power.