“Finding the center of strength within ourselves is in the long run the best contribution we can make to our fellow men.”

Though this statement and a few other variants of it have been widely attributed to Herman Melville, it is actually a paraphrase of one found in a sermon of Henry Melvill, "Partaking in Other Men's Sins", St. Margaret's Church, Lothbury, England (12 June 1855), printed in Golden Lectures (1855) :
: There is not one of you whose actions do not operate on the actions of others—operate, we mean, in the way of example. He would be insignificant who could only destroy his own soul; but you are all, alas! of importance enough to help also to destroy the souls of others. ...Ye cannot live for yourselves; a thousand fibres connect you with your fellow-men, and along those fibres, as along sympathetic threads, run your actions as causes, and return to you as effects.
Misattributed

Foreword (January 1960)
You Learn by Living (1960)
Context: One's philosophy is not best expressed in words; it is expressed in the choices one makes. In stopping to think through the meaning of what I have learned, there is much that I believe intensely, much I am unsure of. In the long run, we shape our lives and we shape ourselves. The process never ends until we die. And, the choices we make are ultimately our own responsibility.

Source: Finding Beauty in a Broken World

Aviation, Geography, and Race (1939)

1950s, Conquering Self-centeredness (1957)
Context: For a long time, man felt that he was the center of the universe and all of his science had given him that. All of the days in the past he came up under what was known as the geocentric theory: the earth was the center of the universe and everything revolved around the earth. Then came Copernicus and Galileo and others, said that the sun is the center, the heliocentric theory came into being. And that reminded us somehow that we are dependent on something. We are not just at the center of this universe. We are only at the center to the extent that we give ourselves and our allegiance to God Almighty. And I’m so glad that the new science came into being to dampen our arrogance. It says to us that our earthly planet is a dependent planet; it is a small planet in the orbits of this universe. The sun is the center of this universe, that man must look beyond himself to discover his significance. And that does something to each of us so that we can see when we have faith in God that we have nothing to boast about, we have nothing to be arrogant about but we live with a humility that keeps us going.

Think Like an Artist (2015)

The trial of Charles B. Reynolds for blasphemy (1887)
Context: Gentlemen, you can never make me believe — no statute can ever convince me, that there is any infinite Being in this universe who hates an honest man. It is impossible to satisfy me that there is any God, or can be any God, who holds in abhorrence a soul that has the courage to express his thought. Neither can the whole world convince me that any man should be punished, either in this world or in the next, for being candid with his fellow-men. If you send men to the penitentiary for speaking their thoughts, for endeavoring to enlighten their fellows, then the penitentiary will become a place of honor, and the victim will step from it — not stained, not disgraced, but clad in robes of glory.
Let us take one more step.
What is holy, what is sacred? I reply that human happiness is holy, human rights are holy. The body and soul of man — these are sacred. The liberty of man is of far more importance than any book; the rights of man, more sacred than any religion — than any Scriptures, whether inspired or not.
What we want is the truth, and does any one suppose that all of the truth is confined in one book — that the mysteries of the whole world are explained by one volume?
All that is — all that conveys information to man — all that has been produced by the past — all that now exists — should be considered by an intelligent man. All the known truths of this world — all the philosophy, all the poems, all the pictures, all the statues, all the entrancing music — the prattle of babes, the lullaby of mothers, the words of honest men, the trumpet calls to duty — all these make up the bible of the world — everything that is noble and true and free, you will find in this great book.
If we wish to be true to ourselves, — if we wish to benefit our fellow-men — if we wish to live honorable lives — we will give to every other human being every right that we claim for ourselves.

The Fall (1956)

Voltaire's Bastards (1992)