ROME – C.S. Lewis famously wrote in The Four Loves, “What draws people to be friends is that they see the same truth. They share it.” That was a philosophical statement for Lewis, but one might say it’s also operationally Pope Francis’s approach to dialogue of all sorts, including the ecumenical push for greater Christian unity.

Next Saturday will bring a classic example of Francis’s “ecumenism of friendship in action,” when the pontiff joins the heads of Christian churches of the Middle East in Bari, Italy, for a day of prayer for peace.

Bari is a natural setting for the initiative. The city’s basilica contains the relics of St. Nicholas, venerated by Catholics and Orthodox alike, making it a popular pilgrimage destination for many Eastern Christians, and it’s long been a rendezvous point for ecumenical encounter. There’s actually an Orthodox chapel inside the Catholic basilica, and Orthodox liturgies are routinely celebrated at an altar by the tomb of St. Nicholas.

As a result, Bari is often described as an ecumenical city “par excellence.”

Francis has invited the patriarchs and heads of all the Eastern churches and Christian communities, Catholic and Orthodox alike, to join him in Bari, whether or not they’re in communion with Rome. At the moment, we don’t yet know who’s coming — most notably, whether Patriarch Kirill of the Russian Orthodox Church, which is legendarily ambivalent about many ecumenical exercises, will take up the pope’s offer.

The closest parallel to the event probably stretches back to 1991, when St. Pope John Paul II invited representatives of the countries involved in the First Gulf War to Rome to join him in prayers for peace. On that occasion, however, it was just the heads of Catholic churches who were on the guest list, not their Orthodox counterparts.

Expecting large crowds, municipal authorities in Bari have announced that certain areas of the city will have only limited access for cars on Saturday, offering incentives for people hoping to take part to use buses and trains.

In the past, ecumenical dialogue has had a largely theological and ecclesiological focus – exploring different concepts of salvation, for instance, or the sacraments, or ordained ministries, or Biblical interpretation. The problem with this approach is that it always seems to put the accent on where the churches disagree, however sincere the desire for common ground may be among those taking part in the exercise.

Francis obviously seems to have a different conception of the path to Christian unity, believing it starts with common action on areas where the churches already agree and have values in common. Evidently, the Middle East is one clear case in point.

Anyone who’s spent much time moving in Christian circles in the Middle East knows the ecumenical bonds among ordinary believers run deep, with many people frankly indifferent to, even at times unaware of, the denominational distinctions that seem to loom so large other places. That sense of common cause is born of a sense of sharing an identity as an embattled minority up against a vast Islamic majority.

As is well known, the Christian population across the region has been declining for some time, and in Iraq and Syria today the threat Christianity faces is existential. In other settings, such as Egypt and Lebanon, sizeable Christian minorities aren’t quite yet on life support, but they face a series of enormous challenges as well as chronic bouts of violence and repression.

Christianity’s oppressors generally make no distinctions among the various branches of the Christian family, and neither do most of the Christians themselves. Francis has referred to this bond any number of times as an “ecumenism of blood.”

As Francis sees it, coming together to do something on behalf of the suffering believers of the Middle East is not only valuable in itself, but it’s also a faster and more reliable route to unity than learned theological debate.

Recently, Archbishop Francesco Cacucci of Bari-Bitonto explained the pope’s ecumenical vision in an essay in a journal called Vita Pastorale, or “Pastoral Life.”

“In the perspective of the Holy Father, communion among the churches isn’t just the fruit of a common yearning and path, but also the drive for a common proclamation of peace,” Cacucci wrote.

The bishop predicted that next Saturday’s common prayer will “help us feel like one Christian people that looks, with the same gaze of faith and love, at the humanitarian tragedy that involves the entire Middle East.”

Cacucci argued that the urgency of the situation in the Middle East, which affects all manner of Christians equally, combined with the ecumenical legacy of Bari, make the July 7 event a potential turning point.

“If in those lands Christians live the ecumenism of martyrdom, because the shedding of Christian blood doesn’t make confessional distinctions, the ‘ecumenism of the people’ in Bari allows us to present to the Lord, united, prayer for the sufferings of life, through the intercession of St. Nicholas the wonderworker.”

It remains to be seen what difference, if any, Saturday’s day of prayer may make for the Middle East, a region which, for reasons both internal and external, seems to have a singular capacity to defy anyone’s efforts at defusing hostilities and bringing peace.

In itself, however, the gathering represents a striking step forward in Francis’s campaign for an ecumenism of friendship, which, as Lewis described, is born of seeing the same truth – and, in this case, wanting to do something together about it.