ABU DHABI, United Arab Emirates — “On the peninsula of the Arabs, two religions shall not co-exist.” So runs a saying traditionally attributed to Omar ibn al-Khattab, one of the Prophet Muhammad’s closest companions and Islam’s second caliph. Omar’s commandment, and others like it, have justified the Muslim faith’s exclusive supremacy on the peninsula for more than 1,400 years.

Well, so much for that.

On Sunday, Pope Francis became the first Catholic pontiff to visit Abu Dhabi, the glittering capital of the United Arab Emirates. In our social-media age, with its endless parade of fleeting images, it’s easy to overlook the significance of this: The vicar of Christ has arrived in Islam’s birthplace — sandy terrain from which Muslims once violently extirpated rival religions.

More than that, Francis is here to celebrate the Mass, the ancient Christian liturgy in which the creator of the universe makes himself mysteriously present under the appearance of bread and wine, per Catholic belief. “For where two or three gather in my name,” Jesus told his followers, “there am I in the midst of them.” The papal Mass here is expected to draw 120,000 faithful.

The invitation to the Holy Father solidifies the UAE’s status as the most responsible power in the Persian Gulf region. And it gives testament to the Emirati leadership’s determination to transcend the bloody, cruel fanaticism that has disfigured the House of Islam and brought ruin to Christians and other minorities unfortunate enough to dwell inside it.

The Emirates’ openness is palpable when you visit the Dubai Mall, where vastly different modes of life — local women with veiled faces, Eastern European tourists with plunging necklines and perilously short skirts, manbun-sporting Arab hipsters and kippah-wearing Orthodox Jews — overlap in safety and peace.

That same civilizational confidence is apparent at the Sheikh Zayed Grand Mosque, the ginormous, Aladdin-style edifice devoted to glorifying Allah — as well as the Emirates’ visionary founder, Sheikh Zayed bin Sultan al-Nahyan. Where else in the Muslim world can you find a mosque that makes a point of putting interfaith outreach at the forefront of its activities? Or a mosque festooned with pictures of the pope and other Christian leaders?

A reform vision defines the UAE’s geopolitical posture as well. Threatened by the expansionist Tehran regime, Abu Dhabi (along with Riyadh) has forged a strategic partnership with Jerusalem that is the region’s worst-kept secret. But in the UAE’s case, the ties go beyond “The enemy of my enemy is my friend.” Since 2010, three Israeli cabinet ministers have visited the UAE to discuss infrastructure, energy and sports.

As Zaki Nusseibeh, a minister of state and adviser to the late Sheikh Zayed, told me: “There is no enmity between us and the state of Israel.”

Opinion polling suggests that the UAE leadership’s enlightened attitudes have begun to filter down to the populace. A YouGov survey conducted ahead of the pope’s visit found that Emiratis are much less likely to be concerned if a close relative marries a Christian than their neighbors in Saudi Arabia and Egypt would be. And while only about a third of Egyptians and Saudis expressed fears about Islamic extremism, more than half of Emiratis did.

YouGov concluded: “UAE results overall are often nearer to that of Western samples than to fellow” Mideast nations “when it comes to general attitudes to world religions.”

Yes, UAE openness befits a federation of commercial city-states, but Westerners tempted to sneer should ask themselves: Which is preferable, the joyful materialism of nouveaux riches Emiratis — or the extremism of the Muslim Brotherhood, Islamic State, Hezbollah, Hamas and other groups of the kind? Which is better for Christians and other regional minorities, not to mention Arabs themselves?

And true, the country isn’t any sort of liberal democracy. Virtually all UAE Muslims, for example, hear the same sermon at Friday prayers — one drafted by a government-approved committee charged with countering radicalism. That goes against every liberal instinct in the West’s bones, but if it means fewer ISIS atrocities here or in our homelands, I’ll take it. The common good isn’t always and everywhere served by our form of government.

That’s an idea the Catholic Church understands deeply, having endured all sorts of powers and principalities for two millennia. Western NGOs and reporters who expect Francis to fulminate against this or that injustice while he’s here forget that the pope brings the deepest reform message of all: the good news of Jesus Christ.

Sohrab Ahmari is op-ed editor of The Post and author of the just-published memoir of Catholic conversion, “From Fire, by Water.”