In 1797, the U.S. Congress ratified the Treaty of Tripoli. This was at a time when the Congress still consisted of many of our founding fathers. It was also a time when the U.S., a country with many Christians, was at odds with an entity consisting largely of Muslims. As part of that treaty these words were included: “the Government of the United States of America is not, in any sense, founded on the Christian religion”. This is from Article 11 of that treaty as signed by John Adams and unanimously ratified by the Senate.
I would suggest that if you were never informed of this part of USA history that your education is a least somewhat deficient. That includes my education which was otherwise pretty good. To learn more about this treaty see Wikipedia. The treaty was replaced a decade later with different wording There are some who say Article 11 is not really part of the treaty but that misses the point. That wording in Article 11 is what was signed by the president and ratified by the U.S. Senate following Constitutional procedures.