“When I was young, I learned a quote in Sunday school that has stayed with me throughout my life. It said, 'teach us to number our days that we gain a heart of wisdom.' * Most of us will wake up 28,762 days- and then one day - we won’t. That means you have about 21,000 days left - and about 14,000 of them for your career. So herein lies the urgency.”

Letter to http://memory.loc.gov/cgi-bin/query/r?ammem/mtj:@field(DOCID+@lit(tj110158)) Thomas Leiper (12 June 1815). Published in The Works of Thomas Jefferson in Twelve Volumes http://oll.libertyfund.org/ToC/0054.php, Federal Edition, Paul Leicester Ford, ed., New York: G. P. Putnam's Sons, 1904, Vol. 11 http://oll.libertyfund.org/Texts/Jefferson0136/Works/0054-11_Bk.pdf, pp. 477–478.
The sentence "I hope our wisdom will grow with our power, and teach us, that the less we use our power, the greater it will be." was used by US-President Barack Obama in his A New Beginning Speech.
1810s
Context: We concur in considering the government of England as totally without morality, insolent beyond bearing, inflated with vanity and ambition, aiming at the exclusive dominion of the sea, lost in corruption, of deep-rooted hatred towards us, hostile to liberty wherever it endeavors to show its head, and the eternal disturber of the peace of the world. In our estimate of Bonaparte, I suspect we differ. [... ] Our form of government is odious to him, as a standing contrast between republican and despotic rule; and as much from that hatred, as from ignorance in political economy, he had excluded intercourse between us and his people, by prohibiting the only articles they wanted from us, that is, cotton and tobacco. Whether the war we have had with England, and the achievements of that war, and the hope that we may become his instruments and partisans against that enemy, may induce him, in future, to tolerate our commercial intercourse with his people, is still to be seen. For my part, I wish that all nations may recover and retain their independence; that those which are overgrown may not advance beyond safe measures of power, that a salutary balance may be ever maintained among nations, and that our peace, commerce, and friendship, may be sought and cultivated by all. It is our business to manufacture for ourselves whatever we can, to keep our markets open for what we can spare or want; and the less we have to do with the amities or enmities of Europe, the better. Not in our day, but at no distant one, we may shake a rod over the heads of all, which may make the stoutest of them tremble. But I hope our wisdom will grow with our power, and teach us, that the less we use our power, the greater it will be.

Book I, Ch. 20
Attributed

America Can Be Saved! (1979) Sword of the Lord Publishers, Murfreesboro, Tennessee, p. 52-53, quoted at "The Rise of the Religious Right in the Republican Party" http://www.theocracywatch.org/schools2.htm

In a Interview With Shirley K. Cohen http://oralhistories.library.caltech.edu/32/1/OH_Patterson.pdf

Esquire interview (2006)

Source: The Sand Pebbles (1962), Ch. 5; speech of Lt. Collins, the commander of the San Pablo to his crew at the start of summer cruising on the Yangtze River
Context: "Tomorrow we begin our summer cruising to show the flag on Tungting lake and the Hunan rivers," he said. "At home in America, when today reaches them, it will be Flag Day. They will gather to do honor and hear speeches. For us who wear the uniform, every day is Flag Day. We pay our honor in act and feeling and we have little need of words. But on this one day it will not hurt us to grasp briefly in words the meaning of our flag. That is what I want to talk about this morning.
"Our flag is the symbol of America. I want you to grasp what America really is," Lt. Collins said, nodding for emphasis. "It is more than marks on a map. It is more than buildings and land. America is a living structure of human lives, of all the American lives that ever were and ever will be. We in San Pablo are collectively only a tiny, momentary bit of that structure. How can we, standing here, grasp the whole of America?" He made a grasping motion. "Think now of a great cable," he said, and made a circle with his arms. "The cable has no natural limiting length. It can be spun out forever. We can unlay it into ropes, and the ropes, into strands, and the strands into yarns, and none of them have any natural ending. But now let us pull a yarn apart into single fibers —" he made plucking motions with his fingers " — and each man of us can find himself. Each fiber is a tiny, flat, yellowish thing, a foot or a yard long by nature. One American life from birth to death is like a single fiber. Each one is spun into the yarn of a family and the strand of a home town and the rope of a home state. The states are spun into the great, unending, unbreakable cable that is America."
His voice deepened on the last words. He paused, to let them think about it....
"No man, not even President Coolidge, can experience the whole of America directly," Lt. Collins resumed. "We can only feel it when the strain comes on, the terrible strain of hauling our history into a stormy future. Then the cable springs taut and vibrant. It thins and groans as the water squeezes out and all the fibers press each to each in iron hardness. Even then, we know only the fibers that press against us. But there is another way to know America."
He paused for a deep breath. The ranks were very quiet.
"We can know America through our flag which is its symbol," he said quietly. "In our flag the barriers of time and space vanish. All America that ever was and ever will be lives every moment in our flag. Wherever in the world two or three of us stand together under our flag, all America is there. When we stand proudly and salute our flag, that is what we know wordlessly in the passing moment....
"Understand that our flag is not the cloth but the pattern of form and color manifested in the cloth," Lt. Collins was saying. "It could have been any pattern once, but our fathers chose that one. History has made it sacred. The honor paid it in uncounted acts of individual reverence has made it live. Every morning in American schoolrooms children present their hearts to our flag. Every morning and evening we render it our military salutes. And so the pattern lives and it can manifest itself in any number of bits of perishable cloth, but the pattern is indestructible."

Poems and Ballads (1866-89), The Triumph of Time
Context: p>We had stood as the sure stars stand, and moved
As the moon moves, loving the world; and seen
Grief collapse as a thing disproved,
Death consume as a thing unclean.
Twain halves of a perfect heart, made fast
Soul to soul while the years fell past;
Had you loved me once, as you have not loved;
Had the chance been with us that has not been.I have put my days and dreams out of mind,
Days that are over, dreams that are done.
Though we seek life through, we shall surely find
There is none of them clear to us now, not one.</p

Paul Flanner, Chapter 16, p. 188
Source: 2000s, Nights in Rodanthe (2002)