It's hard to imagine a less auspicious time for the reception of a papal encyclical on the morally appropriate means of family planning than the summer of 1968. Now, 40 years after it was issued, Pope Paul VI's letter, Humanae Vitae, may finally be getting the hearing it deserves.

Why? Because the developed world is in demographic crisis from decades of plummeting birth rates. Because younger women have figured out a truth that eluded their mothers in the Sixties: the sexual revolution --- made possible in part by easily available contraception --- is great for predatory men, and not-so-great for women. And because John Paul II's "theology of the body" has set the Church's classic teaching in an engaging, humanistic framework.

The Catholic Lite Brigade will doubtless make this anniversary year the occasion to celebrate two generations of theological dissent. Wiser souls will ponder the human wreckage caused by the sexual revolution, especially to women, and think again.

There still remains a lot of confusion about the Church's teaching on marital chastity, in part because most of the Church's ordained leadership has done a poor job of explaining it. Leadership on this front has come primarily from lay scholars and activists --- the formidable Janet Smith, prima inter pares; Richard Doerflinger of the U.S. Conference of Catholic Bishops; now a successor generation, including Christopher West, Helen Alvare, Colleen Carroll Campbell, Pia de Solenni and Mary Eberstadt (whose brilliant article on Humanae Vitae in the August-September First Things is required reading).

Thanks to the brave souls in the natural family planning and new Catholic feminist movements, what Paul VI was trying to say has a chance of being heard --- in part, because it's being said in a vocabulary familiar to 21st century young adults.

It bears repeating yet again, because the mainstream media consistently get it wrong: the Catholic Church does not teach an ideology of fertility-at-all-costs. To the contrary: the Catholic Church teaches that every couple has a moral responsibility to welcome new life as a gift from God, to consider the number of children they can rear and educate, and to order marital life in concert with those two responsibilities.

Where the Church is boldly countercultural is in teaching that the morally appropriate means to regulate fertility is through biology rather than technology. Natural family planning according to the rhythms of biology, the Church proposes, honors the integrity of women and the special nature of the marital bond; natural family planning honors, if you will, the iconography of marital sexual love and its dual nature as both love-sharing and life-giving. Technological means of family planning impede that.

No one imagines that this is easy. But then no one should imagine that marriage is easy, either. The testimony of Catholics who faithfully live the truth about marital love and responsibility is that the rhythms of sexual love and sexual abstinence involved in natural family planning enhance relationships, deepen conversations and enrich marriages humanly and spiritually.

The contempt in which Humanae Vitae and natural family planning are held in some quarters may have less to do with a serious moral appraisal of different methods of family planning than it does with different appraisals of the sexual revolution itself. "Natural," after all, is one of the sacred words of the secular world. So why the tsunami of vitriol thrown at Paul VI and his proposal that natural family planning is the more humane and humanistic approach?

I think it has something to do with the fact that Humanae Vitae laid down a cultural marker: the Catholic Church was not going to cave to the spirit of the age as so many other religious bodies had done. The Catholic Church was not going to declare that sex is just another contact sport: not because the Church is prudish or repressed or misogynist, but because the Church takes men and women seriously, and because the Church imagines the love of Christ for the Church as spousal love. It's a pleasure to discover how many young women get this, today.

George Weigel is Distinguished Senior Fellow of the Ethics and Public Policy Center in Washington, D.C.