[Diamond]

Where does anything say that ours is a Christian nation?

Well, since you ask, and you do use the word "anything" in your interrogatory:

Link

THE UNITED STATES SUPREME COURT

HOLY TRINITY CHURCH v. U.S.

143 U.S. 457, 12 S.Ct. 511, 36 L.Ed. 226

Feb. 29, 1892

Cordially,

[stuartcr]

Sorry, I should have said 'anything official'.