One of the big debates in 19th century was about the (no surprise) the character of religion.
J.S. Mill is an example of is called "natural religion" - meaning that using reason alone, in a priori thought, we can learn about God: who he is, what he does, what he's like. Mill had a lot of company. The idea of "natural religion" was shared by people like Rene Descartes and Thomas Paine. This type of religion is based only on those facts about God which human reason can deduce from pure logical thought. Mill's personal version of natural religion had two interesting features: a great emphasis on hope, and a reminder that there is nothing which forces God to give us a life after this one.
J.S. Mill's essay, “Theism,” is a short work began in 1868 and unfinished when Mill died in 1870. Mill thought that belief in a creator of great power was supported by the design argument, and one could certainly erect the superstructure of hope upon the base of a belief in a creator who would extend human existence beyond the grave: "Appearances point to the existence of a Being who has great power over us — all the power implied in the creation of the Cosmos, or of its organized beings at least — and of whose goodness we have evidence ... ; and as we do not know the limits either of his power or of his goodness, there is room to hope that both the one and the other may extend to granting us this gift provided that it would really be beneficial to us."
Mill continues: "Hope with regard to the government of the universe and the destiny of man after death ... is legitimate and philosophically defensible. The beneficial effect of such a hope is far from trifling." (Mill 1874: 248-9)
On the other hand, people like William Blake embraced what we call "revealed religion" - being skeptical about the powers of human reason to answer all questions. This was a more widely-held view than "natural religion," endorsed by most ordinary people, as well as physicists like Isaac Newton and chemists like Robert Boyle. They thought that human reason was a good and powerful tool, but questioned whether it could know everything, or be the only source of knowledge. In addition to reason, they saw revelation as a source of truth and knowledge - studying sacred texts.
Blake attacked the institutional church, while enthusiastically endorsing the Christian faith. Blake described the ‘everlasting Gospel’, which he saw as the original revelation that he believed Jesus preached. Jesus, for Blake, symbolises the vital relationship and unity between divinity and humanity. One of Blake's strongest objections to traditional churches is that he felt they encouraged the suppression of natural desires and discouraged earthly joy. Blake believed that the joy of man glorified God and that stale religions which deny earthly joy are opposed to God.
These two alternatives - "natural religion" and "revealed religion" - have caused creative thinking in debates over the last two or three centuries. Which one do you like?