The Age of Enlightenment started in the 18th century and gave people a chance to find reason and truth on their own, without the guidance from others. Religion became one the of main targets during this period, because it was a belief that you learned from others. It wasn't proven, it was a set of beliefs and values taught to people with little or no room for own interpretation. The Scientific Revolution in the 17th century brought forth new views on science and skepticism of religion. The philosophers of the time focused on reason and truth. Also during the Reformation religious views were the set of controversy. Both of these eras opened the door for the philosophes during the Age of Enlightenment. .
The philosophes believed that they needed to not only discuss philosophy but also change the world around them. Reason to them was scientific method meant to produce facts from experiences and then reasonableness. Everything was to be rationally criticized, which was the reason religion was a main target. It could not be proven through scientific methods and experiences. While they targeted religion they mostly didn't agree with the fact that religion was not tolerant of other religious beliefs. .
Voltaire was known for his religious toleration and criticized the traditional religious views. He wrote a book called Treatise on Toleration in which he stress the fact that other countries such as Holland and England that practiced religious toleration had no problems. "All men and Brothers under God (Duiker Spielvogel pg530)." He also believed in the idea of Deism. It was based on the Newtonian view that there was a mechanic God who had created the universe. He had no direct involvement in the world and let it run, as it wanted under its laws. Duiker and Spielvogel state that is was a halfway house between religion and disbelief for most philosophes. .
Another philosophe was Denis Diderot.