Late in Oren Jacoby’s valuable documentary “Constantine’s Sword,” the Rome-based Rev. John Pavlowski declares to author and former priest James Carroll, “If you want to make religion a constructive force in society, religions must begin with an honest admission of those moments when they haven’t been a constructive force — when they’ve been a destructive force.”

That is precisely Carroll’s goal and journey in this film, which is inspired by his book of the same title and follows his crusade from Colorado Springs to Rome to Auschwitz-Birkenau to reveal how Christianity became, most poisonously, an enabler and a conduit for anti-Semitism.

Jewish viewers will view “Constantine’s Sword,” which opens July 4 at the Roxie Cinema, with concern for the current activities of evangelicals. More significantly though, they should be enormously grateful for Carroll’s courage and contribution. The movie’s target audience, however, is Christians worldwide, who outnumber Jews about 2 billion to 15 million.

Carroll originally wanted to be a pilot; his father was a high-ranking U.S. Air Force officer. He ended up going to a seminary and becoming ordained, but his anti-Vietnam War activism and other moral conflicts led him to leave the priesthood in 1974 to pursue a career in journalism.

He sets the tone at the outset of the film with the simple but chilling declaration, “I began to see that this cross throws a shadow.”

His first stop is the Air Force Academy in Colorado, which is just down the road from (now-discredited) pastor Ted Haggart’s New Life megachurch. Mikey Weinstein, a Jewish officer and founder of the Military Religious Freedom Foundation, whose three children followed in his footsteps and enrolled at the academy, is appalled at how the tenor of the place has changed in recent years.

One son describes the pressure he felt from other cadets to convert to Christianity. Even more infuriating is his description of finding fliers for “The Passion of the Christ” placed on every plate not just at one meal, but several — this would never have been allowed without the implicit (if not explicit) approval of academy higher-ups.

This section of “Constantine’s Sword” will, or at least should, give pause to Jews who consider the evangelical movement some sort of ally because of its stalwart support of Israel.

Caroll then digs at the roots of Christianity, trying to determine when and how the Jews became demonized as the agents of Christ’s crucifixion, and how religion became allied with armies of violence. With respect to the latter, Carroll and Jacoby devote a good deal of time to the general Constantine, who saw a vision of a cross in the sky (under the influence of what, we can only guess) and had his soldiers weld crosses to their spears.

After his triumph in battle, as emperor he proclaimed of the cross, “By this sign, I have conquered.”

Carroll delves into the Inquisition, of course, introducing us to a Jewish family of ceramics artisans whose ancestors endured the Rome ghetto for three centuries. Their venerable business, they note with pride, is so well regarded that every new pope commissions a set of dishes. One fervently hopes they charge the Vatican top dollar.

The filmmakers’ avenue for exploring the Holocaust is Edith Stein, a Jew who converted and became a nun. Carroll tracks down a copy of a letter she wrote to the pope shortly after Adolf Hitler came to power, warning of the Nazi persecutions and imploring the all-powerful religious leader to intercede. To the contrary, the Vatican was the first foreign power to sign a bilateral treaty with the Nazis.

While both the history lesson and Carroll’s personal journey are fascinating, the film’s best punch is Carroll’s final, no-holds-barred critique of contemporary Christian dogma. He calls on the church to unequivocally rescind the tenets ascribing responsibility for Jesus’ death to the Jews.

If “Constantine’s Sword” has 1 percent of the impact of Mel Gibson’s despicable film, it will be a triumph to savor.

“Constantine’s Sword” opens July 4 at the Roxie Cinema, 3117 16th St., S.F. Tickets: $5-$9. Information: (415) 863-1087 or www.roxie.com.