“If we find, when we read again one of our classics—say Virgil for instance—that we like it better than ever, the experience may suggest an even more pleasing conjecture. Psychologists tell us that fullness of life is the goal of everything that lives, that the impulse towards completeness, towards ripeness and self-realization, is the most compelling of all motives. These discoveries in old books of new beauties and aspects of interest may persuade us, therefore, that we are not only still ourselves, but more ourselves than ever: that our spirit has not only persisted in its being, but has become more lucid in the process.”

1963, Limited Nuclear Test Ban Treaty speech
Context: Continued unrestricted testing by the nuclear powers, joined in time by other nations which may be less adept in limiting pollution, will increasingly contaminate the air that all of us must breathe. Even then, the number of children and grandchildren with cancer in their bones, with leukemia in their blood, or with poison in their lungs might seem statistically small to some, in comparison with natural health hazards. But this is not a natural health hazard — and it is not a statistical issue. The loss of even one human life, or the malformation of even one baby — who may be born long after we are gone — should be of concern to us all. Our children and grandchildren are not merely statistics toward which we can be indifferent.

Variant translations:
What we possess and what gives us strength is our joy in life, our interest in life in all its amoral facets. This is also the foundation for today's art. We do not even know the aesthetic laws.
We are not disillusioned because we have no illusions; we have never had any. What we have, and what constitutes our strength, is our joy in life, in all of its moral and amoral manifestations.
1940 - 1948, Intimate Banalities' (1941)

From Building Blocks for Better Living, pages 65

Writings of the Young Marx on Philosophy and Society, L. Easton, trans. (1967), p. 38
Reflections of a Youth on Choosing an Occupation (1835)

1963, Remarks Prepared for Delivery at the Trade Mart in Dallas
Context: We in this country, in this generation, are — by destiny rather than choice — the watchmen on the walls of world freedom. We ask, therefore, that we may be worthy of our power and responsibility, that we may exercise our strength with wisdom and restraint, and that we may achieve in our time and for all time the ancient vision of "peace on earth, good will toward men". That must always be our goal, and the righteousness of our cause must always underlie our strength. For as was written long ago: "except the Lord keep the city, the watchman waketh but in vain."

Source: Shadow Games (1989), Chapter 5, “Chains of Empire” (p. 30)

Quoted by Diogenes Laërtius; translation from C. D. Yonge (trans.), The Lives and Opinions of Eminent Philosophers (London: H. G. Bohn, 1853), p. 196.
His dying words.