America is in no sense founded on the Christian religion

John 9:41 - Jesus said unto them, If ye were blind, ye should have no sin: but now ye say, We see; therefore your sin remaineth.
America's Christian foundation: You see the Truth, but you won't believe.

What is the origin of the phrase “America is in no sense founded on the Christian religion”? What does it mean?

This quote comes from a line in the Treaty of Tripoli from 1797. While this line is regularly invoked by critics in a futile attempt to prove that America never was a Christian nation, this line is only a small incomplete portion of the full quote. It is taken from a 1797 treaty approved by America in the midst of our first War on Terror against Islamic terrorism. In it, the Muslims acknowledged that America was a Christian nation, and America reminded the Muslims that we were not a European Christian nation with an inherent hostility against Muslims – that is, that we were not a European, Middle-Ages type of Christian nation. By John from Redford
Treaty of Tripoli - ARTICLE 11
As the government of the United States of America is not in any sense founded on the Christian Religion,-as it has in itself no character of enmity against the laws, religion or tranquility of Musselmen,-and as the said States never have entered into any war or act of hostility against any Mehomitan nation, it is declared by the parties that no pretext arising from religious opinions shall ever produce an interruption of the harmony existing between the two countries.