Deism is a category of belief which holds that religious truths should not be arrived at through revelations or authority; rather, these truths should be founded in human reasoning and observation of nature.
The Founding Fathers were devoted readers and followers of some of the great philosophers who advanced the idea of enlightenment, such as Descartes and Voltaire. The idea of enlightenment, which gave rise to Deism, requires that ideas should be supported or analyzed through God given reason. This principle when applied to religion led to the belief that the existence of God can be confirmed through reason and not authority alone, and that God’s revelations are accessible to men. These ideas shaped the thoughts of leaders, such as Thomas Jefferson and Benjamin Franklin, and are also seen to have given them the will to challenge the British through the Declaration and rebelling against the colonial establishment to earn America her independence.
Deism was important historically because it was the faith of many of the Founding Fathers of the United States.
Deism was an Enlightenment idea about religion. It held that God did not actually concern himself with the affairs of people on Earth. Deists were not atheists. They believed that there was a God, but they did not believe (as conventionally religious Christians do) that God involves himself in the lives of people on Earth. Instead, they believed in the idea of God as a "blind watchmaker" who created the universe, set up rules for its functioning, and then left it to go along on its own.