This is a repost of a reply I made, that I think would help to understand why the 2nd Amendment was created and why it's phrased as it is. From our viewpoint, it seems disjunct, but, if you rewind back to life in colonial times, it makes sense.
The sum of the 2nd was the founding fathers were assuring themselves that they could have an Army that drew on civilians in time of need, who owned their own firearms.
Onward ---