This kind of question requires from the teaching authority of the Church a new and deeper reflection on the principles of the moral teaching on marriage—a teaching which is based on the natural law as illuminated and enriched by divine Revelation.

No member of the faithful could possibly deny that the Church is competent in her magisterium to interpret the natural moral law. It is in fact indisputable, as Our predecessors have many times declared, (Popes Pius IX, Pius X, Pius XI, Pius XII, and John XXIII) that Jesus Christ, when He communicated His divine power to Peter and the other Apostles and sent them to teach all nations His commandments (cf. Mt 28:18-19), constituted them as the authentic guardians and interpreters of the whole moral law, not only, that is, of the law of the Gospel but also of the natural law. For the natural law, too, declares the will of God, and its faithful observance is necessary for men’s eternal salvation (cf. Mt 7:21).

In carrying out this mandate, the Church has always issued appropriate documents on the nature of marriage, the correct use of conjugal rights, and the duties of spouses. These documents have been more copious in recent times.

First, let’s define some necessary terms:

• Natural Law: the basic principles of right and wrong that exists in every human person by nature. God created us with these principles in our hearts, and so every human person is capable of knowing these principles.  Pope Leo XIII said, “The natural law is engraved in the soul of every man, because human reason tells him to do good and avoid evil. It has force because it is the voice of a higher reason to which our spirit must submit.”
• Moral law:  The law given to us by God that says “to do what is good and avoid what is evil” (cf. Gaudium et Spes, n. 16).  It is our conscience that urges us to follow this law for it will lead us to Heaven.

Some points to notice:

• The “moral teaching on marriage” is based on natural law.  God teaches us through divine Revelation in the words of Scripture and the teachings of His Church, but the basic principles are known to man naturally.  This includes things such as marriage being between one man and one woman and procreation as the fruit of marriage.  These are common sense things.
• The Church is competent to speak on matters of marriage and family because Jesus Christ Himself gave the Church His authority to teach.  And because the moral law relates to our salvation, the Church is “the authentic guardians and interpreters of the whole moral law”.

Here we get to one of the problems of the day.  There are many, even among Catholics, who don’t see the Church as the authority when it comes to the moral law but only see that Church as one voice among many.  Not to mention that there is also an anti-authoritarian mindset that resides in the modern culture.  We’ve been taught to question and even distrust authority.  People want to trust Jesus but not necessarily the Church that He founded even though it was Jesus who gave the Church His authority.

And so one thing that we have to do help others to see the Church’s role in salvation. What sets the Church apart from “other voices” is that the Church alone has been given her authority by Jesus Christ.  The Church didn’t take it upon herself to teach and interpret moral law.  She was ordained and sent out by God to do so.

So why can the Church answer the questions that the world poses regarding the transmission of life?  Why can the Church declare and teach what is morally good and morally evil?  Because Jesus founded the Church to do just that.

 (Posted with permission from Fr. Lee Acervo at http://fatheracervo.wordpress.com)