It would be incongruous to suppose or suggest the Bill of Rights, including the Second Amendment, which were proscriptions on the powers of the national government, simultaneously acted as a grant of power to the national government. Similarly, as to the term "well regulated," it would make no sense to suggest this referred to a grant of "regulation" power to the government (national or state), when the entire purpose of the Bill of Rights was to both declare individual rights and tell the national government where the scope of its enumerated powers ended.
In keeping with the intent and purpose of the Bill of Rights both of declaring individual rights and proscribing the powers of the national government, the use and meaning of the term "Militia" in the Second Amendment, which needs to be "well regulated," helps explain what "well regulated" meant. When the Constitution was ratified, the Framers unanimously believed that the "militia" included all of the people capable of bearing arms.
George Mason, one of the Virginians who refused to sign the Constitution because it lacked a Bill of Rights, said: "Who are the Militia? They consist now of the whole people." Likewise, the Federal Farmer, one of the most important Anti-Federalist opponents of the Constitution, referred to a "militia, when properly formed, [as] in fact the people themselves." The list goes on and on.