The Founding Fathers lived in a country that was overwhelmingly Christian. The Fathers decided not to try to choose a particular denomination -- they did not want any particular church to be a national, government-approved church. But they knew they lived in a Christian nation. It was all around them. It was so obvious, they didn't need to say anything about it.
But now it has almost all slipped away.
More than that -- our country was overwhelmingly Protestant Christian (if you count Baptists and Quakers as Protestant). It is essentially liberal Roman Catholic and Jewish immigration that has forced the nanny-state concept to displace individual self-reliance as the founding model. IMHO from the records.