[Petrosius]

What the author does not understand is that the "militia" was not just what we call today the National Guard but the entire armed citizenry. From the Militia Act of 1792, Passed May 8, 1792, providing federal standards for the organization of the Militia:

Be it enacted by the Senate and House of Representatives of the United States of America, in Congress assembled, That each and every free able-bodied white male citizen of the respective States, resident therein, who is or shall be of age of eighteen years, and under the age of forty-five years (except as is herein after excepted) shall severally and respectively be enrolled in the militia.

[Svartalfiar]

You're missing part of that act, namely the part that REQUIRES every citizen defined within the act to purchase a firearm.

That every citizen, so enrolled and notified, shall, within six months thereafter, provide himself with a good musket or firelock, a sufficient bayonet and belt, two spare flints, and a knapsack, a pouch, with a box therein, to contain not less than twenty four cartridges, suited to the bore of his musket or firelock, each cartridge to contain a proper quantity of powder and ball; or with a good rifle, knapsack, shot-pouch, and powder-horn, twenty balls suited to the bore of his rifle, and a quarter of a pound of powder; and shall appear so armed, accoutred and provided, when called out to exercise or into service, except, that when called out on company days to exercise only, he may appear without a knapsack.