Abusing the exercise of our freedom and will leads us to develop a rebellious mentality against any authority that tells us to do what is right and avoid what is wrong. Such is a case when Pope Paul VI penned the document "Humanae Vitae", Catholics are expected to receive the moral teaching contained in the document wholeheartedly and without question but instead it was rejected and ridiculed by the majority. The reason why people rebelled against "Humanae Vitae" is that they no longer listen to the voice of the Church but preferred to follow their own passion and listen to their own voices. Some even questioned the authority and competency of the Church in interpreting moral and natural laws. Pope Paul VI long before the release of the document already foreseen the objections that will be raised by liberal clergies and disobedient laity. Thus, in the beginning of the document Pope Paul VI discuss the origin and nature of the Church's authority.
Such questions required from the teaching authority of the Church a new and deeper reflection upon the principles of the moral teaching on marriage: a teaching founded on the natural law, illuminated and enriched by divine revelation. Humanae Vitae No. 4
One of the difficulties why people are having a hard time in accepting the moral teaching of the Church against the use of contraception is that it is no longer relevant in our time. The world is struggling to feed its population and yet every year the world's population is increasing, the only viable solution against the consequences of a ballooning population is to halt its increase by the use of modern methods of contraception. Because of this people are seeing the Church's moral teaching as outdated and out of our league, they now begun to question the origin and foundation of the Church's moral teachings, is it just a teaching of one man or is it willed by God? Pope Paul VI responded by explaining that the Church's teaching against contraception is based on the moral teaching about marriage, marriage is a sacrament willed by God, through marriage the couple is engage into a sacred act of collaborating in God's plan of creation. To employ the use of contraception to impede the cooperation between the married couple and God is a betrayal to the covenant between God and the married couple. The Church's teaching about marriage is no theological speculation, the very fiber of its foundation is the natural law. Natural law encompasses human barrier which means regardless of the person's race, cultural background, religious belief and gender natural law is actively governing our moral compass. Natural law do not change nor evolve like our culture because Natural law emanates from the very being of God, and since God remains to be the same yesterday, today and tomorrow Natural law stays exactly the same, only our understanding and perception of natural law evolves but natural law itself do not. Natural law is not a set of random rules and regulation it is illuminated and enriched by divine revelation in other words it has been revealed to us (Heb.2:1). Basing on this fact the Church's moral teaching against contraception is binding not only to believers but also to non-believers as well.
No believer will wish to deny that the teaching authority of the Church is competent to interpret even the natural moral law. It is, in fact, indisputable, as our predecessors have many times declared, that Jesus Christ, when communicating to Peter and the apostles His divine authority and sending them to teach all nations His commandments, constituted them as guardians and authentic interpreters of all the moral law, not only, that is, of the law of the Gospel, but also of the natural law, which is also an expression of the will of God, the faithful fulfillment of which is equally necessary for salvation. Humanae Vitae No.4
Now, let us turn our attention to the liberal thinkers who without a fail questions the origin of the Church's teaching authority. There is always the tendency among scholars of the sacred art to exalt themselves above the Magisterium, they have often question numerous teachings of the Church that they think are already out of date or needs to be modified in accordance to the modern findings of their scientific research. These so called liberal thinking scholars have forgotten that the Church is more than 2000 years old, as the Church grows older her wisdom also matures and her understanding of God's revelation also deepens and brought to clarity. Should we entrust our salvation to the fallible opinion of scholars regarding divine revelation? Pope Paul VI reiterated a sacred dogma of the Church that Peter being the first pope and his successors and the apostles received a direct mandate from Christ to spread the gospel to all nations (Mt.28:18-20) and in exercise of their ministry they will be having with the divine authority of Jesus Christ (Mt.16:17-19, Papal Bull Unam Sanctam). Since the Bishops as the successors of the apostles in unity with the Pope possesses the divine authority of Jesus Christ they are the only authentic and infallible interpreter of natural moral laws. Any other interpretation aside from what they taught is to be treated as merely a fallible opinion which has no binding authority on us. Magisterial teachings are to be obeyed with great diligence because it is Christ who speaks to us through the Magisterium (Luke 10:16). Henceforth, obedience to the Magisterium is necessary for salvation. In propagation of the good news to all nations the Church's mission is to convey the will of God to the people thus the Church has no authority to alter, modify or change the moral teaching revealed by God to the Church.