In 1998 Pope John Paul II wrote a letter to Dr. Anna Cappella, director of the Center for Research and Study on the Natural Regulation of Fertility at Rome's Catholic University of the Sacred Heart. The occasion was a convention commemorating Humanae vitae, Pope Paul VI's 1968 encyclical. Excerpts are reprinted below.
I hope that everyone will benefit from a closer study of the Church's teaching on the truth of the act of love in which spouses become sharers in God's creative action.
The truth of this act stems from its being an expression of the spouses' reciprocal personal giving, a giving that can only be total since the person is one and indivisible. In the act that expresses their love, spouses are called to make a reciprocal gift of themselves to each other in the totality of their person: nothing that is part of their being can be excluded from this gift. This is the reason for the intrinsic unlawfulness of contraception: it introduces a substantial limitation into this reciprocal giving, breaking that "inseparable connection" between the two meanings of the conjugal act, the unitive and the procreative, which, as Pope Paul VI pointed out, are written by God himself into the nature of the human being (HV, no. 12).
Continuing in this vein, the great pontiff rightly emphasized the "essential difference" between contraception and the use of natural methods in exercising "responsible procreation." It is an anthropological difference because in the final analysis it involves two irreconcilable concepts of the person and of human sexuality (cf. Familiaris consortio, no. 32).
It is not uncommon in current thinking for the natural methods of fertility regulation to be separated from their proper ethical dimension and to be considered in their merely functional aspect. It is not surprising then that people no longer perceive the profound difference between these and the artificial methods. As a result, they go so far as to speak of them as if they were another form of contraception. But this is certainly not the way they should be viewed or applied.
On the contrary, it is only in the logic of the reciprocal gift between man and women that the natural regulation of fertility can be correctly understood and authentically lived as the proper expression of a real and mutual communion of love and life. It is worth repeating here that "the person can never be considered as a means to an end, above all never a means of 'pleasure.' The person is and must be nothing other than the end of every act. Only then does the action correspond to the true dignity of the person." (cf. Letter to Families, no. 12).
The Church is aware of the various difficulties married couples can encounter, especially in the present social context, not only in following but also in the very understanding of the moral norm that concerns them. Like a mother, the Church draws close to couples in difficulty to help them; but she does so by reminding them that the way to finding a solution to their problems must come through full respect for the truth of their love. "It is an outstanding manifestation of charity toward souls to omit nothing from the saving doctrine of Christ," Paul VI admonished (HV, no. 29).
The Church makes available to spouses the means of grace which Christ offers in redemption and invites them to have recourse to them with ever renewed confidence. She exhorts them in particular to pray for the gift of the Holy Spirit, which is poured out in their hearts through the efficacy of their distinctive sacrament: this grace is the source of the interior energy they need to fulfill the many duties of their state, starting with that of being consistent with the truth of conjugal love. At the same time, the Church urgently requests the commitment of scientists, doctors, health-care personnel and pastoral workers to make available to married couples all those aids which prove an effective support for helping them fully to live their vocation (cf. HV, no. 23-27).