Ireland was thus one of the last Western democracies decriminalize consensual sexual activity between adult gay men. That it may now consolidate same-sex marriage as the new normal in the developed world is striking evidence of how quickly and profoundly attitudes have changed. If it happens, it will owe much to two circumstances, one great and epic, the other small and intimate.

Few democracies have ever seen such a close alignment of religious and political power as Ireland after independence. The new state was overwhelmingly Roman Catholic and deeply identified with the church. For decades, almost all political parties followed church teaching on “moral” questions and inscribed that teaching in law.

Contraceptives were fully legalized only in 1985. Divorce was outlawed until a narrowly approved referendum in 1995. Ireland’s abortion laws are still so restrictive that they allow almost no exceptions, even for rape, incest or fatal fetal abnormalities.

Yet the church’s power proved immensely damaging to those who once wielded it. Its arrogance resulted in the catastrophic scandals of church leaders’ covering up decades of child abuse by priests and religious orders. The church’s moral authority has largely collapsed in Ireland.

As a result, its ability to influence the referendum on same-sex marriage is limited. Many church leaders have avoided taking a hard line. This owes something to Pope Francis’s more conciliatory tone on homosexuality, but even more to an awareness that many of the faithful, like Ms. O’Connor, no longer take church teaching on sexuality as gospel. The archbishop of Dublin, Diarmuid Martin, went so far as to warn church leaders not to use “language which is insensitive and over-judgmental” — a warning surely rooted in his understanding of the other, more personal force in this debate.

Changes in attitudes to L.G.B.T. people have been driven by one overwhelming factor: Once people were out of the closet, they were not “them” but “us” — family, friends, neighbors. This is a powerful force in a close-knit country like Ireland.

Ireland doesn’t always function well at the level of large institutions, but the Irish tend to be good at social relations. If they know you, they want to think well of you.