Thoughts on the wording of the Second Amendment
The immediate ancestor of the Second Amendment is the Virginia ratifying convention's demand for a bill of rights, which asked for a guarantee that:
"That the people have a right to keep and bear arms; that a well regulated Militia composed of the body of the people trained to arms is the proper, natural and safe defence of a free State."
The ancestors of that were in turn three State guarantees. First, Virginia's 1776 Declaration of Rights, which praised the militia but had no right to arms proviso:
"That a well regulated militia, composed of the body of the people, trained to arms, is the proper, natural, and safe defence of a free state..."
And Pennsylvania's 1776 Declaration, which had a right to arms but no militia clause:
"That the people have a right to bear arms for the defence of themselves and the state..."
And finally Massachuetts' 1780 Declaration (which added "keep" and "for the common defense"):
:The people have a right to keep and to bear arms for the common defence."
Thought: when the Framers (to be precise, the Virginia ratifying convention) worked from the existing State models, they chose the broadest wording of each. From PA came the right to bear arms. From MA came the right to keep (but with the addition of "for the common defense" trimmed out). From VA came the militia clause (which neither PA nor MA had). In each case, the broadest wording available was chosen.