As our colleague Christopher White was on the ground in Geneva on Thursday covering Pope Francis’s visit to the World Council of Churches, Inés San Martín and I were in Rome watching the live stream of the events and trying to provide back-up.

During a morning prayer service, I found myself struck by the wildly different types of Christianity represented in the room, from low-church Protestantism to smells-and-bells Orthodox. I remarked that it was like a spiritual rainforest, with all the various species on display.

Without missing a beat, San Martín, watching Francis taking his place on the dais, shot back: “Yeah, and the King of the Jungle just walked into the room.”

Though perhaps without intending it, the one-liner she delivered actually amounts to a great answer to an obvious question: If the pope loves the World Council of Churches so much, then why isn’t the Catholic Church a member?

Founded in 1948, the World Council of Churches (WCC) includes most of the Oriental Orthodox Churches, most of the Eastern Orthodox Churches, most of the mainline Protestant churches, several Anglican churches (including the Church of England), and some, though by no means all, Evangelical and Pentecostal churches.

In effect, the WCC is an assembly of most major forms of Christianity outside the Catholic Church.

All in, there are perhaps 250 million Orthodox Christians in the world, 85 million Anglicans, and some 900 million Protestants – over 1.2 billion believers in total, though not all represented in the WCC. However, that vast pool of people is divided among a bewildering variety of denominations – in the WCC, it’s 349 in all – so no one church can claim a following anywhere close to the sum of the parts.

The Catholic Church, however, which counts about 1.4 billion followers worldwide, is institutionally one, all united – in however fissiparous or notional a fashion – under the leadership of one figure, the pope.

To be sure, there are multiple reasons why the Catholic Church doesn’t belong to the WCC. In 1969, when Pope Paul VI visited the WCC himself, he said the time for membership was not yet “ripe” and that any path to formal membership likely would be “long and difficult.” In the almost 50 years since that moment, Catholicism’s observer status with the WCC would seem to have become more or less a permanent condition.

Part of the reason for that is doctrinal and ecclesiological. From the official Catholic point of view, the ultimate aim of the press for Christian unity is to put Humpty-Dumpty back together again under the aegis of the papacy – a reformed papacy, perhaps, along the lines suggested by St. Pope John Paul II in his 1995 encyclical letter Ut Unum Sint, one rooted in the conception of primacy of the first millennium, but still with the Petrine Ministry at the center.

The WCC, on the other hand, strikes some Catholics as embodying a sort of confederate Christianity without any clear center, implying a false equality among various Christian options and risking diluting Catholic beliefs about apostolic succession, ministries, the sacraments, and many other core doctrinal principles.

Moreover, some Catholic critics of the WCC note that it’s basically a debating society with no legislative power whatsoever. Its Faith and Order Commission, for instance, has put out lofty documents on liturgy, baptism, the Eucharist, and any number of other subjects, but it’s generally difficult to know to what extent its member churches actually accept and endorse those texts. There’s no penalty for non-compliance, no enforcement mechanism, and for some, that leaves open the question of exactly what the point of spending time and resources to produce those texts actually is.

However, there’s another way to read the Catholic Church’s decision to remain a non-member that puts the accent less on criticism and skepticism than on respect and deference.

Here’s the raw truth: The pope – any pope – is, by far, the most recognizable, consequential, and powerful religious leader in the world. The Catholic Church is, by far, the most vertically integrated Christian church in the world, and the Vatican, despite its small physical footprint, is the most important “soft power” in the global community of nations.

If the Catholic Church were to join the WCC, therefore, it would immediately become the dominant force in the organization, essentially blotting other Christian traditions and actors out of the sky.

Moreover, the Vatican’s personnel, infrastructure and organizational capacities would, almost irresistibly, become the spinal column of the WCC, meaning that the organization, for all practical purposes, would risk becoming just another department of the Roman Curia, the central administrative bureaucracy of the Vatican in terms of governance of the universal Church.

In effect, should a pope decide to become a formal member of the WCC, there’s a very real possibility that he would end up drowning out the voice of other forms of Christianity in order to augment it – an ecclesiastical form, in some ways, of destroying the village in order to save it.

In the run-up to Francis’s trip to Geneva on Thursday, some observers were wondering if the pontiff would pull yet another rabbit out of his hat and announce that the time had “ripened” and Catholicism would join the WCC. In the end, of course, he came and went without doing that.

These considerations suggest, however, that the fact the pope didn’t take the plunge on membership doesn’t necessarily mean his heart wasn’t in it – it could simply mean that he has too much respect for the group to subsume it.