Political Disquisitions (1774)
Context: That government only can be pronounced consistent with the design of all government, which allows to the governed the liberty of doing what, consistently with the general good, they may desire to do, and which only forbids their doing the contrary. Liberty does not exclude restraint; it only excludes unreasonable restraint. To determine precisely how far personal liberty is compatible with the general good, and of the propriety of social conduct in all cases, is a matter of great extent, and demands the united wisdom of a whole people. And the consent of the whole people, as far as it can be obtained, is indispensably necessary to every law, by which the whole people are to be bound; else the whole people are enslaved to the one, or the few, who frame the laws for them.
“In a State or Assemblage of People that live together in a Community, where there are Laws, Liberty can only consist in doing that which every One ought to do, and not to be constrained to do that which One ought not to do.”
Item 37
Proposals for a New Law Code (1768)
Help us to complete the source, original and additional information
Catherine the Great 29
Empress of Russia 1729–1796Related quotes

“That one hundred and fifty lawyers should do business together ought not to be expected.”
On the U.S. Congress, in his Autobiography (6 January 1821)
1820s

Statement published in A Year of Beautiful Thoughts (1902) by Jeanie Ashley Bates Greenough, p. 172, Third statement for June 11. This has often been misattributed to Helen Keller in some published works since at least 1980, perhaps because she somewhere quoted it.
Variant:
I am only one,
But still I am one.
I cannot do everything,
But still I can do something;
And because I cannot do everything,
I will not refuse to do the something that I can do.
The Book of Good Cheer : A Little Bundle of Cheery Thoughts (1909) by Edwin Osgood Grover, p. 28; also in Masterpieces of Religious Verse (1948) by James Dalton Morrison, p. 416, where it is titled "Lend a Hand"

Entry (1955)
Eric Hoffer and the Art of the Notebook (2005)
Context: Our doubts about ourselves cannot be banished except by working at that which is the one and only thing we know we ought to do. Other people's assertions cannot silence the howling dirge within us. It is our talents rusting unused within us that secrete the poison of self-doubt into our bloodstream.

Fragment on Government http://quod.lib.umich.edu/l/lincoln/lincoln2/1:261?rgn=div1;view=fulltext (1 July 1854?) in "The Collected Works of Abraham Lincoln", ed. Roy P. Basler, Vol. 2, pp. 220-221
1850s
Context: The legitimate object of government, is to do for a community of people, whatever they need to have done, but can not do, at all, or can not, so well do, for themselves - in their separate, and individual capacities. In all that the people can individually do as well for themselves, government ought not to interfere. The desirable things which the individuals of a people can not do, or can not well do, for themselves, fall into two classes: those which have relation to wrongs, and those which have not. Each of these branch off into an infinite variety of subdivisions. The first - that in relation to wrongs - embraces all crimes, misdemeanors, and nonperformance of contracts. The other embraces all which, in its nature, and without wrong, requires combined action, as public roads and highways, public schools, charities, pauperism, orphanage, estates of the deceased, and the machinery of government itself. From this it appears that if all men were just, there still would be some, though not so much, need for government.

“They never will love where they ought to love, who do not hate where they ought to hate.”

Sect. V : An Enquiry into the Duty of Christians in general, and what Means ought to be used, in order to promote this Work.
An Enquiry into the Obligations of Christians (1792)
Context: Many can do nothing but pray, and prayer is perhaps the only thing in which Christians of all denominations can cordially, and unreservedly unite; but in this we may all be one, and in this the strictest unanimity ought to prevail. Were the whole body thus animated by one soul, with what pleasure would Christians attend on all the duties of religion, and with what delight would their ministers attend on all the business of their calling.
We must not be contented however with praying, without exerting ourselves in the use of means for the obtaining of those things we pray for. Were the children of light, but as wise in their generation as the children of this world, they would stretch every nerve to gain so glorious a prize, nor ever imagine that it was to be obtained in any other way.

Roberts v. Plant (1895), L. R. 1 Q. B. D. [1895], p. 603.