It was an article of Thomas Jefferson’s faith that no government should interfere in anyone’s private religious beliefs. A passionate student of history, Jefferson knew that religious struggles through the ages had caused “rivers of blood” to flow all over the world.

The blood is still flowing. News of sectarian violence reaches us daily from across the globe, bringing us unimaginably horrific and mind-numbing images. One of Jefferson’s most fervent hopes was that Americans would be spared this carnage, and he did his best to set us on that path. It’s worth pausing, this Fourth of July, to ponder this facet of Jefferson’s deep wisdom, and how well we’ve lived up to it.

Jefferson believed the best way to ensure that both peace and religious liberty could flourish would be to educate citizens to avoid violent disagreements over trivial doctrinal distinctions through a constitutional regime that prevented government from favoring one set of religious beliefs over another.

He discovered how hard it was to divorce religion from politics during his bid for the presidency in 1800. He had what today we’d call “a religion problem.” By the mid-1790s, he had developed a reputation as a faithless philosopher, even an atheist, certainly not a Christian. This was a grave matter, for religious beliefs then, as now, are often conflated with character. Nervous New Englanders and his enemies in the Federalist Party took this notion to heart; rumors spread that Jefferson planned to outlaw the Bible.

On his watch, they said, incest and adultery would run rampant. He betrayed his true sentiments, they claimed, by his ardent support of the French Revolution, which sought to eradicate religion in France. Their talking point was clear: Jefferson’s atheism disqualified him from the presidency. ...