Christ In Winter: Reflections on Faith for the Years of Winter
I think it is quite clear that the USA was founded on Christian principles. That does not mean, though, that the writers of the Constitution intended to create a Christian nation.
When Moses Seixas wrote to George Washington and asked if the First Amendment meant Jews would be tolerated in the new nation, Washington replied, No. Jews would not be tolerated. Tolerance meant that a majority group would put up with a minority group. The First Amendment meant not that Jews would be tolerated, but that they would be free, in the same way any other citizen was free. Any citizen of any religion, or none, had the same rights as any other. 
That is a Christian principle. All people have total worth in the eyes of God, and each person is to be treated as a child of God. “Do unto others as you would have them do unto you.” Not “Do unto CHRISTIANS…” but “Do unto OTHERS…”
The fact that the US is founded on Christian principles does not mean that we are “a Christian nation.” It means the exact opposite.
Being a Christian nation, as currently defined in political rhetoric means either that all citizens must be Christian, or that Christians are the majority group and may, or may not, put up, with non-Christians, may or may not “tolerate” them.
Strangely, people who champion the Christian nation idea refer to themselves often as “strict constitutional Constructionists” who believe in “the original intent of the Constitution writers.” They seem to think that they know the intent of the Constitution writers better than George Washington did.
1] From Sarah Vowell, LAFAYETTE N THE SOMEWHAT UNITED STATES, p. 266 in the LP edition.
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