ROME – One of the main achievements of the Second Vatican Council in the mid-1960s was to find a theological logic for the widespread popular desire to break down the walls between the various Christian churches, and to usher in a new era of dialogue and partnership that’s come to be known as “ecumenism.”

Vatican II did so by elaborating a new theology of the church: While the fullness of the church, according to Catholic doctrine, may exist only in Catholicism, there are nevertheless precious elements of it to be found outside that deserve honor and respect.

With that, the world changed. Before Vatican II, many Catholics hesitated to even enter a Protestant church; afterwards, such taboos were gone. While ecumenism hasn’t yet achieved full reunion, it’s still among the most stunningly successful Christian movements of the late 20th century.

Without overdramatizing things, something similar may be going at the 2014 Synod of Bishops on the family vis-à-vis people living in what the church considers “irregular” situations – cohabitating couples, gays and lesbians, people who divorce and remarry outside the church, and so on.

Heretofore, the usual Catholic rhetoric about such folks has been that they’re “living in sin.” The synod has clearly rejected that sort of barb, saying instead that the Catholic Church must be a “welcoming home.”

On same-sex unions, for instance, the Synod of Bishops has yet to issue any sort of pointed criticism of gay marriage. It has, however, brought an absolute novelty – today, a senior cardinal stood on Rome’s biggest stage at the moment and said that the church needs to see the positive value in committed same-sex relationships, including instances of “mutual aid to the point of sacrifice” that is a “precious support in the life of the partners.”

None of this means that Catholic doctrine is on the brink of changing, as the synod has made clear that’s not in the cards. It may, however, augur a new era of what might be called “lifestyle ecumenism,” in which the church approaches people living outside its ideal for marriage with friendship rather than condemnation.

Underlying that press is a similar Copernican revolution in theology.

As Cardinal Péter Erdő of Hungary made clear today in his speech summarizing the opening round of discussion, upholding church teaching on marriage does not exclude “the possibility of recognizing positive elements even in the imperfect forms that may be found” in other relationships.

Repeated references during the synod to the “law of graduality” cut in the same direction, since they imply acceptance that people move towards moral ideals through different stages and at different paces. The fact that someone may be in a situation less than what the church considers ideal therefore doesn’t mean that there’s no moral value at all in their current circumstances.

In other words, just as Vatican II taught that elements of truth and holiness can be found outside the Catholic Church, in other Christian denominations and even in other religions, the Synod of Bishops seems to be saying there are pieces of truth and holiness outside Catholic marriage in all sorts of other relationships.

It remains to be seen whether that insight will have a similar transforming effect on the way Catholicism engages the outside world. Like the original ecumenical vision of Vatican II, however, it does seem to correspond to a widely held hunger at the grassroots for a new way of relating to people in unconventional family situations.

Lifestyle ecumenism, in other words, may well be the real theological breakthrough at the 2014 Synod of Bishops. If so, it would be a fitting evolution under Pope Francis, the pope whose most famous sound-bite is, “Who am I to judge?”