I’d agree it’s wrong to say our country was founded on Christian principals. It’s also wrong to dismiss the faith of many of our founders and Christianity’s influence. You have Paine who was the only FF antagonistic towards faith. Franklin and Jefferson were deist and have a mismatch of quotes that contradict. But you also have dozens who were faithful and fervent believers, even ministers. So, they were strongly influenced by their faith and were well aware that they were governing a Christian people. By today’s standards Franklin and Jefferson would be viewed as men of faith. it’s only against the backdrop of their time and positioned against those like Patrick Henry or John Jay.
Christian practice was so normally integrated into everyday life no one thought twice about using government buildings for worship. Prayer was common if not always practiced in sessions of Congress.
The fundamentals of independence that the nation stands on are our basic human rights being endowed by our creator. That was something all the FFs proudly signed. Wisely, they made sure that the government could not institute or coerce the practice of religion, which is fundamentally contrary to Christian belief. Having seen, first hand, the affect of such abuse in England and across Europe they acted accordingly.