The book, "The birth of an encyclical," was written by Gilfredo Marengo, a professor of theological anthropology at the John Paul II Pontifical Theological Institute.
To compile it, Marengo was given access to documents from the archive of the Vatican's Secretariat of State. He needed a special permission from the pope, since the Holy See's archives are usually available only after 70 years.
The book presents a series of drafts and instructions, as well as a previously unpublished encyclical draft titled De nascendi prolis. That draft was totally replaced by the text that became Humanae vitae.
Parolin retraced Paul VI's "suffering path" in the drafting of the encyclical.
"Paul VI," Parolin said, "looked at Humanae vitae as an immediate development of new and authoritative words that the Second Vatican Council was able to express on marriage and family."
According to the cardinal, the Second Vatican Council recognized that marriage and family were "at the top of the list of the issues for the presence of the Church in the world." Parolin noted that John Paul II and Benedict XVI emphasized the importance of the family during their pontificates, as Pope Francis has also done.
Parolin said that the Church's approach to birth control was "at the beginning focused on the concern for the possible spread of anti-natalist policies," and after that there was "the consideration that the obligation to follow moral principles was the only path to make the Church convincing in the world."
However, Cardinal Parolin noted, "these two position cannot be imposed in abstract way," but they must be harmonized with "an pastoral – ecclesial wisdom that cannot be found in many of the protagonists of those years.
Cardinal Parolin referred indirectly to the heated discussion that anticipated the publication of the encyclical. The so-called majority report of the commission, in favor of the use of contraceptive pill under certain conditions, was leaked to the press, and published simultaneously in April 1967 in the French newspaper Le Monde, the English magazine The Tablet, and the American newspaper the National Catholic Reporter.
Cardinal Karol Wotjytla, the future St. John Paul II, was a member of the drafting committee, though he was unable to take part to the meetings personally.
After Humanea vitae was published, Cardinal Wojtyla even asked Pope Paul VI to draft an instruction to explain that what was contained in Humanae vitae has always been part of the Church's magisterium, and affirm its infallibility.
Such a position shows how the discussion was developing.
St. Paul VI's figure stands in the midst of this discussion. Cardinal Parolin noted that "texts published and commented in Marengo's book clarify that the Pope had no doubts about the doctrinal contents of the encyclical, and deny the myth of an uncertain and Hamletic Paul VI."
Paul VI was rather concerned to find "adequate ways" to present the Church's teaching, Parolin said. This was reason the pope waited for five years before publishing the encyclical.