By the time of the American Revolution, less than half of the population are attending established churches. In Virginia, it’s less than a third. The Founding Fathers, those who write the Declaration, Constitution, and its amendments, have to please both the faithful, and the faithless.
Thomas Jefferson (the first US Secretary of State, its second Vice President, and third President) and John Adams (the first US Vice President and its second President) are two of the most influential authors on the Declaration of Independence. But their religious views differ greatly.
John Adams believes the state has no power without the moral authority of Christianity and Jefferson believed that the new state of America should be guided by the morality of Christianity, but not be regulated by its religion.
The compromise between Jefferson and Adams partially resolves itself with the federal first amendment, in that it still allows individual states to increase the influence of religion.