It is true that the US Founders were religious. But, they had a different understanding of religion that we have today.
When discussing religion, it is imperative to realize that "religion" is one of those broad terms that has a different meaning to different people. People at different times in history had different views of religion. For most of history, the term "religion" referred to one's highest thoughts. They applied the term "superstition" to things believed that were untrue.
The modern definition of religion is closer to the traditional definition of "superstition."
If I defined "religion" to mean everything that people believed throughout time that proved untrue; then, yes, religion is a silly thing. But what about the beliefs that I currently hold true? What about beliefs that actually are true?
If I held "religion" to mean my highest thoughts (which is closer to the traditional definition) and called my false beliefs superstition; then religion is a good thing while superstition is still a bad thing.
One of the odd things about logic is that it is possible to derive truth from myth. It is also possible to derive false beliefs from valid scientific observations. (This is a long post unto itself).
Personally, I find claims of non-religion absurd. Claims of non-religion begin with a person's assertion of what is true and what is not true (a religion). The anti-religious zealot then creates a hihgly parsed definitions of religion which is essentially the same as the traditional definition of "superstition."
This game of changing terms is called equivocation. Modern thinkers like to call it sublation.
The term "religion" often mixes in with our personal aspirations. For example, a person seeking power might come to see religion as a path to power. If a power monger is not positioned to use religion for power, the power monger is prone to reject religion as an obstacle to power.
Conversely, a person seeking freedom might come to see religion as a path to freedom. But if religion is being used for oppression, the same person might come to see established religion as a obstacle to freedom.
Since people tend to project their worst traits on others, the definition of religion because even more strained. If I am seeking to use religion (or irreligion) in my quest for power, I will project negative images on the religions of others.
People with a ruling class mentality are prone to see religion as a way to subdue the masses and to justify their actions. Machiavelli taught the prince to appear religious without actually being religious.
Prior to the US Revolution, the monarchs used a distortion of religion to claim authority from an ancient covenant that stretched back to the patriarchs of ancient Israel. Many monarchs were Machiavellian and hid their atrocities under the guise of religion
After the revolution, there was a flurry to create new religions as a new generations of power mongers sought to gain authority over others. The French Revolution saw both the invention of new religions and reactionary anti-religions
In philosophy the term "modern" refers to the school of thought following Kant (1724-1804). Modernism is actually centuries old. The US Founders had a classical liberal education and world view. Modernism swept the world in the early 1800s.
Hegel (1770-1831) is perhaps the most influential modern philosopher. Hegel created a modern logic to replace classical logic. Hegel also created a "Philosophy of History" that presented the Germanic people (and their king) as the leading character on the world stage. Hegel was immensely popular in the US. American Pundits in the early 1800s sought ways to position White-Anglo-Saxon-Protestants as the new master race. People made all sorts of bizarre claims to a new covenant that stretched back to ancient Israel.
Hegelians were trying to create a new radicalized philosophical religion.
A Young Hegelian named Ludwig Feuerbach (1804-1872) created a radicalized anti-religion, which took things a step further.
Since anti-religion is a religion, anti-religion leads to an endless stream of clever sounding paradoxes. It is a form of the reflexive paradox (modern dialectics).
The US Founders were religious. Their thoughts on religion were profoundly different than those about religion today. They were part of a classical liberal tradition. This tradition combined Aristotelian, Judeo/Christian and nascent scientific thought in the pursuit of individual liberty.
There was a radicalization of religion (and anti-religion) that took place between us and them. Today religion is seen in the light of a never-ending culture war.
To make matters worse, in recent years we've seen a strong trend to commercialize all religious holidays. The commercial Easter is about bunnies, chocolate eggs and treasure hunts.
I wanted to write a post to wish everyone a glorious Easter Weekend. The Passover and Easter are highlights of the Judeo/Christian calendar. The Passover remembers a flight from bondage. Easter remembers the crucifixion and resurrection of Christ. The crucifixion took place in the generations following the transition of the Roman Republic into the Roman Empire. The Romans were crucifying people by the thousands.
These are both extremely important ideas in the evolution of Western thought. Both events involve the people faced with a tyrannical government.
The culture wars of the Modern Era have put so many blinders and filters on these important events that it is often difficult to derive meaning from them.
As we celebrate and think about the Passover and Easter, I find it worthwhile to think about how different people at different times perceived these events.