“The origins of secularism in the west may be found in two circumstances—in early Christian teachings and, still more, experience, which created two institutions, Church and State; and in later Christian conflicts, which drove the two apart. Muslims, too, had their religious disagreements, but there was nothing remotely approaching the ferocity of the Christian struggles between Protestants and Catholics, which devastated Christian Europe in the sixteenth and seventeenth centuries and finally drove Christians in desperation to evolve a doctrine of the separation of religion from the state. Only by depriving religious institutions of coercive power, it seemed, could Christendom restrain the murderous intolerance and persecution that Christians had visited on followers of other religions and, most of all, on those who professed other forms of their own.Muslims experienced no such need and evolved no such doctrine. There was no need for secularism in Islam, and even its pluralism was very different from that of the pagan Roman Empire, so vividly described by Edward Gibbon when he remarked that "the various modes of worship, which prevailed in the Roman world, were all considered by the people, as equally true; by the philosopher, as equally false; and by the magistrate, as equally useful." Islam was never prepared, either in theory or in practice, to accord full equality to those who held other beliefs and practiced other forms of worship. It did, however, accord to the holders of partial truth a degree of practical as well as theoretical tolerance rarely paralleled in the Christian world until the West adopted a measure of secularism in the late-seventeenth and eighteenth centuries.”

You Can Lead an Atheist to Evidence, But You Can't Make Him Think (2009)

Hindu Temples – What Happened to Them, Volume II (1993)

The Kingdom of God is Within You (1894)

Hindu Society under Siege (1981, revised 1992)

Book III, Chapter 12, "Faith"
Mere Christianity (1952)
Context: There are two parodies of the truth which different sets of Christians have, in the past, been accused by other Christians of believing: perhaps they may make the truth clearer. One set were accused of saying, "Good actions are all that matters. The best good action is charity. The best kind of charity is giving money. The best thing to give money to is the Church. So hand us over ₤10,000 and we will see you through." The answer to that nonsense, of course, would be that good actions done for that motive, done with the idea that Heaven can be bought, would not be good actions at all, but only commercial speculations. The other set were accused of saying, "Faith is all that matters. Consequently, if you have faith, it doesn't matter what you do. Sin away, my lad, and have a good time and Christ will see that it makes no difference in the end." The answers to that nonsense is that, if what you call your "faith" in Christ does not involve taking the slightest notice of what he says, then it is not Faith at all—not faith or trust in Him, but only intellectual acceptance of some theory of Him.

History of Hindu-Christian Encounters (1996)

The Social History of Art, Volume I. From Prehistoric Times to the Middle Ages, 1999, Chapter IV. The Middle Ages

John Adams, letter to Thomas Jefferson (16 July 1814). From the Works of John Adams, Vol. X http://books.google.com/books?id=9G0vAAAAYAAJ&dq=works%20of%20john%20adams%20%22volume%20x%22&pg=PA100#v=onepage&q&f=false, p. 100
1810s

Source: 1930s- 1950s, The End of Economic Man (1939), p. 50