From Pope St. John Paul II’s Apostolic Exhortation Familiaris Consortio (1981):
Precisely because the love of husband and wife is a unique participation in the mystery of life and of the love of God Himself, the Church knows that she has received the special mission of guarding and protecting the lofty dignity of marriage and the most serious responsibility of the transmission of human life.
Thus, in continuity with the living tradition of the ecclesial community throughout history, the recent Second Vatican Council and the magisterium of my predecessor Paul VI, expressed above all in the Encyclical Humanæ vitæ, have handed on to our times a truly prophetic proclamation, which reaffirms and reproposes with clarity the Church’s teaching and norm, always old yet always new, regarding marriage and regarding the transmission of human life.
For this reason the Synod Fathers made the following declaration at their last assembly: “This Sacred Synod, gathered together with the Successor of Peter in the unity of faith, firmly holds what has been set forth in the Second Vatican Council (cf. Gaudium et spes, 50) and afterwards in the Encyclical Humanæ vitæ, particularly that love between husband and wife must be fully human, exclusive and open to new life (Humanæ vitæ, 11; cf. 9, 12).”83
83 Propositio 21. Section 11 of the encyclical Humanæ vitæ ends with the statement: “The church, calling people back to the observance of the norms of the natural law, as interpreted by her constant doctrine, teaches that each and every marriage act must remain open to the transmission of life (ut quilibet matrimonii usus ad vitam humanam procreandam per se destinatus permaneat)”: Acta Apostolicæ Sedis 60 (1968), 488.
— Familiaris Consortio 29