Deism was a theological movement that grew in the 17th and 18th centuries and was particularly popular in England. They affirmed the existence of a Creator (as distinct from atheists) but denied revelation, even in many cases the Divine origin of the Scriptures. This view had been taken by the Spiritualists in the 16th century, but they had dismissed the Bible as a "paper pope" and professed allegience to their "inner light" - the Deists, on the other hand, professed allegience only to that which could be proven by reason and empricism. In his The Reasonableness of Christianity, as Delivered in the Scriptures (1695), John Locke had declared that the Gospel was compatible with reason - the logical conclusion for the next generation was that those parts not compatible with reason must be discarded. Five years before The Reasonableness of Christianity, Locke had published An Essay concerning Human Understanding, which had split human knowledge into two categories - that which was a matter of revelation (of this one could be certain), and that established by the senses (of this one could be certain to a degree of probability). But among the former nothing could be admitted that was contrary to reason. "How a rational man," opined Locke,
that should enquire and know for himself, can content himself with a Faith or Religion taken upon trust . . . is to me astonishing.
Locke's Baconian rationalism became a potent tool in the hands of the Deists. Locke himself had noted some problems with the Scripture - he remained silent on the matter of the Trinity, and did not believe that Jesus Christ came to absolve mankind of its sins. The point of Christ's coming was to provide a new torch of reason and cast away the vices of the priesthood, who had "excluded reason from having any thing to do with religion." Locke said that Jesus had never assumed the role of priest nor alluded to a priesthood, in which may be discerned the anti-clericalism that was the Zeitgeist in late 17th century England. Locke had established a link between reason and revelation, accepting in principle the subordination of the latter to the former. The Deists were even more radical in that they went on to attack Scripture and revelation itself.
Just as God had provided men with the facility for knowing what benefitted or caused harm to their physical body - pleasure and pain - surely he would not have been so absent-minded as to leave them incapable of discerning their spiritual well-being. The faculty provided by God for man to know his Creator and the way to Salvation was, said the Deists, reason. The "Book of Nature", ie. empirical observation of the natural world, was sufficient to know God's will. This had only been subverted by vile "priestcraft" - which was taken to be actively malevolent, the means by which the priesthood tried to enslave man and promote its arbitrary power. The Divine status of Scripture began to come under fire. How could a reasonable man think God would first reveal his will through the book?, asked Matthew Tindal. What of the virtuous pagans who had lived and died before Jesus, and the millions who had never heard God's Word? Locke had used natural law to save their souls, but the Deists had no such faith. Clearly, if the Word was needed to save souls, then millions of pagans would go without Grace. This was not compatible with reason and God's infinite goodness.
Most of the received tradition of the Jewish and Christian faiths was superstition, said the Deists. They set about demonstrating what they believed were the psychological reasons for people lapsing so easily into superstition - evidently the machinations of the priests were not sufficient alone. Using Lockean empiricism, they explained how sometimes people became cut off from their sensory apparatus out of fear for what it might tell them, and aliented from reason likewise. At times like these - most of the lives of primitive peoples - they would accept tradition and ritual as a replacement for reason if doing so proved more comfortable. Belief in miracles fell into a similar category - and many Deists denied that miracles were occuring in the World of the day, as people said they were. And if they accepted this, it was also unlikely that miracles also took place in Palestine over a millenia and a half ago - another attack on Scripture. Miracles in the Bible had to be interpreted spiritually and not literally to have meaning.
Deism was very influential in the 17th and 18th centuries, colouring the views of many people in what is now called the Enlightenment. It tied in neatly with the popular rationalism and empiricism of the day and the fashionable snobbery towards superstition that was at the time popular. Particularly in England - the nation par excellence of freedom and religious toleration - Deism was identified with the patriotism of the people in being free from all manner of evil Popery and delusions. It of course came under attack from religious conservatives - Protestants and Catholics alike - who sniffed in it, not without reason, the destruction of their entire system of belief. Likewise, Locke's silence on the Trinity meant that Deism was often tainted in many people's eyes by an association with Arianism or Unitarianism, faiths which denied the Divinty of Christ altogether.
It also eventually helped give rise to pandeism, a movement which combined deism and pantheism, and about which more can be learned in the write-ups in that node.