It is important to remember context. The founding fathers had seen all manner of weapons banned by government(s), and as a result, the most common use of standing armies was against the citizens, not other armies.
Arms was inclusive and not an exclusive concept, and would have covered every weapon known at the time; from the quarterstaff to the pike, from the sword to the battleaxe, and from the musket to the cannon.
This was to guarantee that the first right of free speech be upheld as well as the other rights that were endowed by the Creator...and this was the critical concept: Man's rights came from God and could not be curtailed by government. This is why the Founders required a moral, religious people.
John Locke wrote many essays that provided the groundwork for our Founder's philosophy of government. One of those was "A Letter Concerning Toleration". Some of the key principles were that different religions be allowed equally because they espoused moral, ethical behavior, and that the "church" be expelled from political authority; for example, people were going to prison for missing church.
Locke proposed men be allowed to practice the religion of their choice: freedom of religion. Note that he never suggested freedom from religion. In fact, the only class of people who were not to be tolerated were the Atheist; for he had no moral or ethical basis for his creed or his behavior, and could not be trusted.
