I suspect Jefferson agreed entirely with that concept.
You can have your religious beliefs, and you can participate in public life influenced by those beliefs. And the result of your public participation may be that the state has certain policies and laws. But the state may not favor any religion nor require religion nor prohibit religion nor permit any religion to exert any authority over it nor ascribe any authority whatsoever to any religion's established body of laws. IOW, there must be a wall.
It's a bit paradoxical, but I think most Americans can grasp the idea, if they try. Of course, the details, the details ... I.e., the state is required to be secular, but somehow the end result nevertheless ends up looking like America without any righteous minorities feeling screwed. Or something like that.
I think we need to remember that our constitution was based on certain negative principles. There would be no king, no nobility, no state Church. Likewise there would be no metropolis, like Paris and London, that could dominate the country. Congress is not, like the king in parliament, unlimited in its law-making ability. As time has worn on, many of these principles have been undermined by a concentration of wealth and power not unlike that which marked 18th Century England.