The Catholic Church is the only Church that has its own moral theology. One reason for this has to do with the several different expressions or functions of her authority. For instance, the Church speaks on Christ’s behalf through the ordinary prophetic office of the pope and his encyclicals, through the prophetic office of bishops in union with the pope, and through the teachings of the General Councils (i.e. Nicea, Trent and the First and Second Vatican Council). In addition, Catholic believers look to the Church Fathers, the Doctors of the Church and canonized Saints for moral clarity. From these sources a systematic moral teaching had developed over the last two thousand years. As such, moral teachings misrepresenting the Catholic Faith were more easily detected and denounced.
However, other Christian denominations and non-Christian religions do not enjoy these sources of authority and guidance. Furthermore, many, if not, most religions rely on personal interpretations of the moral law and/or they consider morality to be subjective, that is, a matter of personal opinion. If then a moral teaching has only the authority of personal opinion or biblical interpretation, then such a teaching can be just as easily dismissed by personal opinion. With this, unity of thought and consistency through time is all but impossible.
Whether non-Catholics agree with the Catholic Church's teachings or not, at least in the mind of faithful Catholics, the above mentioned sources of authority are believed to be the expression of Christ's prophetic voice on earth. Because these sources are credible to members of the Church, a union of minds and a uniformity of action can be realized.
A second reason why the Catholic Church has her own moral theology has to do with what Christ taught her about morality. Far from being arbitrary or the product of the human imagination, the Church teaches that the truth can be known about what is right and what is wrong because moral principles are real; that is to say, they exist independent of human likes or dislikes. Another way to put it is that the moral law has everything to do with the purpose God created human beings for. Because human beings have a purpose, it follows that actions such as sex and relationships such as marriage have a specific, definable purpose. Eliminate God from the equation then morality is believed to be a product of convention or consensus. With this, morality can only be man-made and therefore changeable.
Contrary to secular-liberal thought, right is right even when no one is right and wrong is wrong even when everybody is wrong. Hence, no consensus or majority vote can change the moral law. Indeed, there are certain actions that are intrinsically wrong. For that reason they can never be justified.
It is not enough to know the basics of Catholic moral theology. It is also important to articulate its superiority over predominant influence of secular-liberalism or even conservatism. Again, the essential difference between Catholic moral teaching and what the society teaches about morality revolves around the idea of purpose: the purpose of life, the purpose of institutions and the purpose of actions. As such, Catholic morality is a movement towards something definite. For instance, in Catholic moral theology, sex has two specific goals: love and procreation as designed by God. This is why sex belongs in a certain context, namely, the life-long commitment of marriage. But for many secular minded people, sex can be as meaningless as a recreational event and nothing more.
It is important to remember that secular-liberalism (the modern belief that we can be happy without God and hence define our own morality) is a movement away from something; a reaction, if you will. Even for mere pleasure seekers, it is a protest against anything that puts limitations on their so-called freedoms. According to most people who subscribe to this view, no human person or human action is invested with any inherent or divine purpose. As such, the morality of sex, the morality of procreation and even the morality of dying is wholly dependent on individual decision-making. In fact, the greatest offense against secular-liberalism is to definitively declare that sexual activity outside of marriage is morally wrong and an offense against God. This is why we hear many who are persuaded by this worldview say, "Who are you to judge?" In other words, since morality- especially sexual morality -cannot be determined or known we are in no position to criticize or condemn such behavior.
Next: Morality 101: Some basics you may have forgotten