VATICAN CITY — Pope Francis, cardinals and bishops from around the world have gotten an unexpected lecture on the joys of sex, from a Catholic couple brought in to talk about what makes a marriage last.

Ron and Mavis Pirola, parents of four from Sydney, Australia, told a Vatican gathering of some 200 prelates that sexual attraction brought them together 57 years ago and that sex has helped keep them married for 55 years.

“The little things we did for each other, the telephone calls and love notes, the way we planned our day around each other and the things we shared were outward expressions of our longing to be intimate with each other,” the couple said in a joint statement to the closed meeting late Monday.

“Gradually we came to see that the only feature that distinguishes our sacramental relationship from that of any other good Christ-centered relationship is sexual intimacy, and that marriage is a sexual sacrament with its fullest expression in sexual intercourse.”

The audience of celibate men was a bit taken aback. “That’s not what we bishops talk about mostly, quite honestly,” a sheepish British Cardinal Vincent Nichols told reporters Tuesday. ”But to hear that as the opening contribution did, I think, open an area … and it was a recognition that that is central to the well-being of marriage often.”

Francis called the two-week meeting of bishops to try to figure out how to make church teaching on a host of Catholic family issues – marriage, divorce, homosexuality and yes, sex – more relevant to today’s Catholics. The debate will continue in October, 2015, and culminate when Francis issues recommendations offered by the synod.

Several of the bishops complained that the Vatican’s own teachings on sexual matters are often impenetrable to ordinary people. The Vatican’s main document on sex, the 1968 encyclical Humanae Vitae, lays out the church’s opposition to artificial contraception with complicated moral theological arguments and 41 footnotes.

The Pirolas told the gathering that they occasionally read church documents on family matters, “but they seemed to be from another planet, with difficult language and not terribly relevant to our own experiences.”