It's a shame that I've been to quite a few Theology of the Body congresses and only now have I actually sat down and read Paul VI's Humanae Vitae. It's short and very clear. It is amazing to think how counter-cultural he had to be to publish it. I still remember standing in Fatima and hearing the story of how he caught an express plane to Fatima months before publishing it to seek special intercession and guidance. Here are some of my favorite quotes.
But the most remarkable development of all is to be seen in man's stupendous progress in the domination and rational organization of the forces of nature to the point that he is endeavoring to extend this control over every aspect of his own life—over his body, over his mind and emotions, over his social life, and even over the laws that regulate the transmission of life. (n. 2)
The question of human procreation, like every other question which touches human life, involves more than the limited aspects specific to such disciplines as biology, psychology, demography or sociology. It is the whole man and the whole mission to which he is called that must be considered: both its natural, earthly aspects and its supernatural, eternal aspects. (n. 7)
Though this fidelity of husband and wife sometimes presents difficulties, no one has the right to assert that it is impossible; it is, on the contrary, always honorable and meritorious. (n. 9)
But to experience the gift of married love while respecting the laws of conception is to acknowledge that one is not the master of the sources of life but rather the minister of the design established by the Creator. (n. 13)
In preserving intact the whole moral law of marriage, the Church is convinced that she is contributing to the creation of a truly human civilization. She urges man not to betray his personal responsibilities by putting all his faith in technical expedients. (n. 18)