“In the tradition of the ancients and of many great thinkers of our race, I am a Deist. Echoing the words of far greater thinkers than myself, I see an intelligent motivating force throughout the universe and behind Nature's Laws.”

The Principles of Success in Literature (1865)
Context: Except in the rare cases of great dynamic thinkers whose thoughts are as turning-points in the history of our race, it is by Style that writers gain distinction, by Style they secure their immortality. In a lower sphere many are remarked as writers although they may lay no claim to distinction as thinkers, if they have the faculty of felicitously expressing the ideas of others; and many who are really remarkable as thinkers gain but slight recognition from the public, simply because in them the faculty of expression is feeble. In proportion as the work passes from the sphere of passionless intelligence to that of impassioned intelligence, from the region of demonstration to the region of emotion, the art of Style becomes more complex, its necessity more imperious.

Progress In Religion (2000)
Context: I am saying to modern scientists and theologians: don't imagine that our latest ideas about the Big Bang or the human genome have solved the mysteries of the universe or the mysteries of life. Here are Bacon's words again: "The subtlety of nature is greater many times over than the subtlety of the senses and understanding". In the last four hundred years, science has fulfilled many of Bacon's dreams, but it still does not come close to capturing the full subtlety of nature.

Education (1902)
Context: I am not of those who believe in lackadaisical methods. On the contrary, I advocate a vigorous, thorough, exact mental training which shall fit the mind to expand upon and grasp large things and yet properly to perceive in their just relation the significance of small ones to discriminate accurately as to quantity and quality and thus to develop individual judgment, capacity and independence.
But at the same time I am of those who believe that gentleness is a greater, surer power than force, and that sympathy is a safer power by far than is intellect. Therefore would I train the individual sympathies as carefully in all their delicate warmth and tenuity as I would develop the mind in alertness, poise and security.
Nor am I of those who despise dreamers. For the world would be at the level of zero were it not for its dreamers gone and of today. He who dreamed of democracy, far back in a world of absolutism, was indeed heroic, and we of today awaken to the wonder of his dream.

Source: The Outsider (1956), p. 158

Source: White Oleander

Interview http://americanindian.net/asimov.html in Southwest Airlines Magazine 1979)
General sources

The Other World (1657)
Context: According to your religion, is any part of the body more sacred or unholy than another? Why will I commit a sin if I touch myself on the part in the middle and not when I touch my ear or heel? Because it tickles? Then I should not defecate into a pot, because that can't be done without some sort of sensual pleasure. Nor should mystics elevate themselves to the contemplation of God, because they enjoy a great pleasure of imagination. I am indeed astounded at how much the religion of your country is against nature and is jealous of all the pleasures of men. I am surprised that your priests haven't made it a crime to scratch oneself, because one feels a pleasurable pain.
And yet I have noticed that far-seeing Nature has made all great, brave and intelligent people favor the delicacies of love: witness Samson, David, Hercules, Caesar, Hannibal and Charlemagne. Did Nature do so in order that they might harvest the organ of that pleasure with a sickle? Alas, Nature even went under a washtub to debauch Diogenes, who was thin, ugly and flea-bitten, and make him compose sighs to Lais with the breath he blew upon carrots. No doubt Nature did so because it was concerned lest there be a shortage of honorable people in the world.

It's An Interconnected World (2002)