It can be instructive to consider what the influential people at the time the Constitution was written thought about the right to keep and bear arms:
Americans have the right and advantage of being armed - unlike the citizens of other countries whose governments are afraid to trust the people with arms.
-- James Madison, The Federalist Papers
"The best we can hope for concerning the people at large is that they be properly armed."
-- Alexander Hamilton, The Federalist Papers at 184-188
"One of the ordinary modes, by which tyrants accomplish their purposes without resistance, is, by disarming the people, and making it an offense to keep arms."
-- Constitutional scholar and Supreme Court Justice Joseph Story, 1840
Men trained in arms from their infancy, and animated by the love of liberty, will afford neither a cheap or easy conquest.
-- From the Declaration of the Continental Congress, July 1775.
"As to the species of exercise, I advise the gun. While this gives [only] moderate exercise to the body, it gives boldness, enterprise, and independence to the mind. Games played with the ball and others of that nature, are too violent for the body and stamp no character on the mind. Let your gun, therefore, be the constant companion to your walks."
-- Thomas Jefferson, writing to his teenaged nephew.
The right of the citizens to keep and bear arms has justly been considered as the palladium of the liberties of a republic; since it offers a strong moral check against usurpation and arbitrary power of rulers; and will generally, even if these are successful in the first instance, enable the people to resist and triumph over them."
-- Supreme Court Justice Joseph Story of the John Marshall Court
Militias, when properly formed, are in fact the people themselves and include all men capable of bearing arms. [...] To preserve liberty it is essential that the whole body of the people always possess arms and be taught alike, especially when young, how to use them.
-- Senator Richard Henry Lee, 1788, on "militia" in the 2nd Amendment
No kingdom can be secured otherwise than by arming the people. The possession of arms is the distinction between a freeman and a slave.
-- "Political Disquisitions", a British republican tract of 1774-1775
Are we at last brought to such a humiliating and debasing degradation, that we cannot be trusted with arms for our own defence? Where is the difference between having our arms in our own possession and under our own direction, and having them under the management of Congress? If our defence be the *real* object of having those arms, in whose hands can they be trusted with more propriety, or equal safety to us, as in our own hands?
-- Patrick Henry, speech of June 9 1788
"To disarm the people... was the best and most effectual way to enslave them."
-- George Mason, speech of June 14, 1788
"The great object is, that every man be armed. [...] Every one who is able may have a gun."
-- Patrick Henry, speech of June 14 1788
Such are a well regulated militia, composed of the freeholders, citizen and husbandman, who take up arms to preserve their property, as individuals, and their rights as freemen.
-- "M.T. Cicero", in a newspaper letter of 1788 touching the "militia" referred to in the Second Amendment to the Constitution.
That the said Constitution shall never be construed to authorize Congress to infringe the just liberty of the press or the rights of conscience; or to prevent the people of the United states who are peaceable citizens from keeping their own arms...
-- Samuel Adams, in "Phila. Independent Gazetteer", August 20, 1789
The danger (where there is any) from armed citizens, is only to the "government*, not to *society*; and as long as they have nothing to revenge in the government (which they cannot have while it is in their own hands) there are many advantages in their being accustomed to the use of arms, and no possible disadvantage.
-- Joel Barlow, "Advice to the Privileged Orders", 1792-93
[The disarming of citizens] has a double effect, it palsies the hand and brutalizes the mind: a habitual disuse of physical forces totally destroys the moral [force]; and men lose at once the power of protecting themselves, and of discerning the cause of their oppression.
-- Joel Barlow, "Advice to the Privileged Orders", 1792-93
The whole of the Bill [of Rights] is a declaration of the right of the people at large or considered as individuals... It establishes some rights of the individual as unalienable and which consequently, no majority has a right to deprive them of.
-- Albert Gallatin, Oct 7 1789
Before a standing army can rule, the people must be disarmed, as they are in almost every kingdom in Europe. The supreme power in America cannot enforce unjust laws by the sword, because the people are armed, and constitute a force superior to any band of regular troops.
-- Noah Webster
The right of self-defense is the first law of nature: in most governments it has been the study of rulers to confine this right within the narrowest limits possible. Wherever standing armies are kept up, and when the right of the people to keep and bear arms is, under any color or pretext whatsoever, prohibited, liberty, if not already annihilated, is on the brink of destruction."
-- Henry St. George Tucker (in Blackstone's Commentaries)
"Rightful liberty is unobstructed action, according to our will, within limits drawn around us by the equal rights of others."
-- Thomas Jefferson
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
-- Benjamin Franklin, Historical Review of Pennsylvania, 1759.