“Whereas civil rulers, not having their duty to the people duly before them, may attempt to tyrannize, and as the military forces which must be occasionally raised to defend our country, might pervert their power to the injury of their fellow citizens, the people are confirmed by the article in their right to keep and bear their private arms.”

2000s, 2003, Invasion of Iraq (March 2003)

p. 691-692

Statement to a reporter in the Boston Record, 14 April 1903. (quoted in Alpheus Thomas Mason, Brandeis: A Free Man's Life (1946), p. 122.)
Commonly paraphrased as "The most important office is that of the private citizen" or "The most important political office is that of the private citizen", and sometimes misattributed to his dissenting opinion in Olmstead v. United States.
Extra-judicial writings

letter to the German rulers (1524), as quoted in The History of Compulsory Education in New England, John William Perrin, 1896

An Examination of the Leading Principles of the Federal Constitution (1787).

Essay, written under the pseudonym "Candidus," in The Boston Gazette (14 October 1771), later published in The Life and Public Services of Samuel Adams (1865) by William Vincent Wells, p. 425
Context: The liberties of our Country, the freedom of our civil constitution are worth defending at all hazards: And it is our duty to defend them against all attacks. We have receiv'd them as a fair Inheritance from our worthy Ancestors: They purchas'd them for us with toil and danger and expence of treasure and blood; and transmitted them to us with care and diligence. It will bring an everlasting mark of infamy on the present generation, enlightened as it is, if we should suffer them to be wrested from us by violence without a struggle; or be cheated out of them by the artifices of false and designing men. Of the latter we are in most danger at present: Let us therefore be aware of it. Let us contemplate our forefathers and posterity; and resolve to maintain the rights bequeath'd to us from the former, for the sake of the latter. — Instead of sitting down satisfied with the efforts we have already made, which is the wish of our enemies, the necessity of the times, more than ever, calls for our utmost circumspection, deliberation, fortitude, and perseverance. Let us remember that "if we suffer tamely a lawless attack upon our liberty, we encourage it, and involve others in our doom." It is a very serious consideration, which should deeply impress our minds, that millions yet unborn may be the miserable sharers of the event.

The Labour Party in Perspective (Left Book Club, 1937).
1930s

Virginia Resolution of 1798 (24 December 1798) http://www.constitution.org/cons/virg1798.htm
Federalist No. 46 (29 January 1788) Full text at Wikisource
1790s
Variant: [The Constitution preserves] the advantage of being armed which Americans possess over the people of almost every other nation (where) the governments are afraid to trust the people with arms.
Context: That the General Assembly doth particularly protest against the palpable and alarming infractions of the Constitution, in the two late cases of the "Alien and Sedition Acts" passed at the last session of Congress; the first of which exercises a power no where delegated to the federal government, and which by uniting legislative and judicial powers to those of executive, subverts the general principles of free government; as well as the particular organization, and positive provisions of the federal constitution; and the other of which acts, exercises in like manner, a power not delegated by the constitution, but on the contrary, expressly and positively forbidden by one of the amendments thereto; a power, which more than any other, ought to produce universal alarm, because it is levelled against that right of freely examining public characters and measures, and of free communication among the people thereon, which has ever been justly deemed, the only effectual guardian of every other right.
Context: Besides the advantage of being armed, which the Americans possess over the people of almost every other nation, the existence of subordinate governments, to which the people are attached, and by which the militia officers are appointed, forms a barrier against the enterprises of ambition, more insurmountable than any which a simple government of any form can admit of. Notwithstanding the military establishments in the several kingdoms of Europe, which are carried as far as the public resources will bear, the governments are afraid to trust the people with arms.

Roberts v. Gwyrfai District Council (1899), L. R. 2 C. D. 614.