“Faith, hope, love, and insight are the highest achievements of human effort. They are found-given-by experience.”

"Tamerlane", l. 177 (1827).

From a speech on the state of the Middle East, September 10, 1968 http://www.jewishvirtuallibrary.org/jsource/US-Israel/lbjpeace1.html
1960s

Optimism (1903)
Variant: Optimism is the faith that leads to achievement

"The Case for Comedy", Lanterns & Lances http://books.google.com/books?id=m0RZAAAAYAAJ&q=%22humor+and+pathos+tears+and+laughter+are+in+the+highest+expression+of+human+character+and+achievement+inseparable%22&pg=PA143#v=onepage (1961); previously appeared in The Atlantic Monthly November 1960 http://books.google.com/books?id=6q8GAQAAIAAJ&q=%22and+pathos+tears+and+laughter+are+in+the+highest+expression+of+human+character+and+achievement+inseparable%22&pg=PA98#v=onepage
From Lanterns and Lances‎

Source: The Art of Loving (1956)
Context: To speak of love is not "preaching," for the simple reason that it means to speak of the ultimate and real need of every human being. That this need has been obscured does not mean it does not exist. To analyze the nature of love is to discover its general absence today and to criticize the social conditions which are responsible for this absence. To have faith in the possibility of love as a social and not only exceptional-individual phenomenon, is a rational faith based on the insight into the very nature of man.

Credo (1965)
Context: I believe that love is the main key to open the doors to the "growth" of man. Love and union with someone or something outside of oneself, union that allows one to put oneself into relationship with others, to feel one with others, without limiting the sense of integrity and independence. Love is a productive orientation for which it is essential that there be present at the same time: concern, responsibility, and respect for and knowledge of the object of the union.
I believe that the experience of love is the most human and humanizing act that it is given to man to enjoy and that it, like reason, makes no sense if conceived in a partial way.

What is Art? (1897)
Context: Humanity unceasingly strives forward from a lower, more partial and obscure understanding of life to one more general and more lucid. And in this, as in every movement, there are leaders — those who have understood the meaning of life more clearly than others — and of those advanced men there is always one who has in his words and life, manifested this meaning more clearly, accessibly, and strongly than others. This man's expression … with those superstitions, traditions, and ceremonies which usually form around the memory of such a man, is what is called a religion. Religions are the exponents of the highest comprehension of life … within a given age in a given society … a basis for evaluating human sentiments. If feelings bring people nearer to the religion's ideal … they are good, if these estrange them from it, and oppose it, they are bad.

"The Holy Dimension", p. 333
Moral Grandeur and Spiritual Audacity: Essays (1997)

Beware of Pity (1939)