From Reynolds v. U.S., 1878
Reynolds argued that as a Mormon, it was his religious duty to practice polygamy if possible.
In its ruling, the U.S. Supreme Court considered the history of religious freedom in the U.S. and quoted Thomas Jefferson’s letter: he stated that there was a distinction between religious belief and any action that flowed from it. The former “lies solely between man and his God,” so “the legislative powers of the government reach actions only, and not opinions.”
If polygamy were allowed, said the court, someone might eventually argue that their religion required human sacrifice, and “to permit this would be to make the professed doctrines of religious belief superior to the law of the land, and in effect to permit every citizen to become a law unto himself.” Therefore the spirit of the First Amendment was that Congress could not legislate against opinion, but could legislate against action.