I have read the relevant Papers. That's not quite what it says. It says the militia is drawn from the citizenry. But it isn't necessarily the whole citizenry, hence the term "well-regulated" in the 2A. A mob is not "well-regulated".

Scalia himself in Heller said the term "milita" was obsolete, and that service in a "militia" was unnecessary to the right to bear arms. Basically, he said "the first 13 words don't count". (Yeah, a real originalist.) Militias were all the rage before Heller, with folks thinking that if they could say they were in a "militia" then the gummint couldn't grab their guns. There are still some, but after Heller a lot of them just went home and stopped playing "army" in the woods.

We've already been over national defense, and the vision that citizen militias would be the go-to. So I won't recapitulate that. The only bit that is still relevant is that some were concerned the people would need to "defend themselves" against the federal (i.e. the anti-federalists).