ISTANBUL, Turkey — Observers of the Christian landscape have long said we’re living in a basically post-denominational age, in which the differences between churches are no longer nearly as critical as the rifts within them.

Today, an Evangelical Protestant and a conservative Catholic may feel they have more in common with each other than with other members of their own churches, while an eco-friendly “green” Orthodox Christian may feel greater kinship with a like-minded Methodist than with an ultra-traditional Orthodox monk on the Greek island of Mount Athos.

As a result, the most arduous form of ecumenism today often isn’t between churches, but rather within one’s own house.

On the second day of his trip to Turkey, Pope Francis delivered a strong message of unity that was ostensibly about the first sort of ecumenism, meaning the press for better relations among churches and rites, but which also seemed to carry implications for the second.

Diversity, Francis said, “may seem to create disorder,” but that’s where faith in the Holy Spirit enters the picture.

“Under his guidance, [differences] constitute an immense richness,” he said, “because the Holy Spirit is the Spirit of unity, which is not the same thing as uniformity.”

Earlier in the day, Francis provided an impressive visual of unity by pausing in Istanbul’s famed Blue Mosque alongside the Grand Mufti of Istanbul for a moment of silent prayer, repeating a gesture from Pope Benedict XVI in 2006 that was hailed as turning point in Christian/Muslim relations.

Later on Saturday, the pope celebrated a Mass at Istanbul’s Cathedral of the Holy Spirit, which was “inter-ritual” in the sense that it brought together Syrian, Armenian, and Chaldean Catholics, as well as members of the Latin rite that’s most familiar to Catholics in the West. Also on hand were a number of Orthodox dignitaries, including Patriarch Bartholomew of Constantinople.

That mix of rites and confessions naturally elicited reflections from the pontiff on unity and diversity. The message had clear relevance, because relations among the various Catholic rites and churches in the Middle East are notoriously fractious.

On background, local sources in Istanbul said those tensions flared up anew in the behind-the-scenes preparation for Saturday’s Mass.

Representatives of one church reportedly demanded more tickets to the liturgy than another, on the grounds that their following in Turkey is slightly larger. There were also spats over seating arrangements, especially whose clergy and VIP attendees would claim the first row.

Anyone who’s been following recent events in the Catholic Church, however, will recognize that the pope’s injunction on Saturday has much broader applications.

For instance, the recent Synod of Bishops on the family in the Vatican exposed deep internal fissures on a variety of fronts, including how welcoming the Church ought to be to gays and lesbians, how positive its evaluation of various “irregular” relationships such as living together outside marriage should be, and whether Catholics who divorce and remarry outside the Church ought to be allowed to receive Communion.

Inside and outside the synod hall, debates took on a sometimes nasty tone, featuring accusations of gag orders and censorship, suspicions that the deck was being stacked in one direction or another, and charges that some synod leaders were deliberately imposing their own views on its documents rather than reflecting the consensus of the group.

That synod was merely a preparation for another, larger summit in October 2015, with the year in between serving as a period of reflection — which, depending on how things play out, could mean that the divisions that erupted last time have a full year to fester before returning with even greater force.

Given that context, the pope’s words seemed to have a wider scope. In effect, Francis argued that coping with such divisions takes faith.

“Only the Holy Spirit is able to kindle diversity, multiplicity, and, at the same time, bring about unity,” Francis said.

“When we try to create diversity, but are closed within our own particular and exclusive ways of seeing things, we create division,” he said. “When we try to create unity through our own human designs, we end up with uniformity and homogenization.”

It doesn’t have to be that way, the pope argued.

“If we let ourselves be led by the Spirit, richness, variety, and diversity will never create conflict, because the Spirit spurs us to experience variety in the communion of the Church,” Francis said.

The pontiff conceded that unity may not be an easy sell.

“The temptation is always within us to resist the Holy Spirit, because he takes us out of our comfort zone and unsettles us,” he said. “It is always easier and more comfortable to settle in our sedentary and unchanging ways.”

Francis called believers to avoid the tug of defensiveness.

“Our defensiveness is evident when we are entrenched within our ideas and our own strengths — in which case we slip into Pelagianism — or when we are ambitious or vain,” he said.

(Pelagianism was an early Christian heresy which held that believers could earn salvation through their own efforts, rather than depending on the grace of God.)

“These defensive mechanisms prevent us from truly understanding other people and from opening ourselves to a sincere dialogue with them,” the pope said.

“The Church, flowing from Pentecost, is given the fire of the Holy Spirit, which does not so much fill the mind with ideas, but enflames the heart,” Francis said. “She is moved by the breath of the Spirit which does not transmit a power, but rather an ability to serve in love, a language which everyone is able to understand.”

Time will tell if that call to embrace diversity and to shun defensiveness has any traction, especially by holding Catholicism together ahead of the next Synod of Bishops.

In the meantime, Francis returns to the traditional form of ecumenism Saturday night, leading a joint prayer service with Patriarch Bartholomew at the Phanar, the headquarters of the Ecumenical Patriarchate of Constantinople, and then joining him for an Orthodox liturgy Sunday morning.

In brief comments to reporters Saturday afternoon, Bartholomew called the pope’s visit to the headquarters of his church a “historic moment.”

“We will pray together for the unity of our churches, for divided Christendom, as well as for peace in the Middle East and around the globe,” Bartholomew said. “We try to have close collaboration to face together the acute problems of the present world.”

The two leaders are scheduled to sign a joint declaration Sunday morning, which will pledge the Catholic and Orthodox churches to continue the press for closer ties.