[Error condemned:] 56. The laws of morals by no means need divine sanction, and there is not the least need that human laws conform to the natural law, or receive the power of binding from God.

[Error condemned:] 57.The science of philosophy and of morals, likewise the civil laws, can and should ignore divine and ecclesiastical authority. (Denzinger-Hünermann 2956-2957. The Syllabus of errors condemned by Pius IX, December 8, 1864)

After almost twenty centuries, the gravest situations and problems that humanity has to face do not change; in fact, Christ always occupies central place in history and in life: men  either adhere to Him and His Church, and thus  enjoy light, goodness, right order, and the benefits of peace, or they live without Him or fighting against Him, and deliberately remain outside His Church, and so among them there is confusion, mutual relations become difficult, and the danger of bloody wars looms over them. (John XXIII. Address on the solemn opening of the Second Vatican Council, October 11, 1962)

Therefore the Church announces the good tidings of salvation to those who do not believe, so that all men may know the true God and Jesus Christ whom He has sent, and may be converted from their ways, doing penance. To believers also the Church must ever preach faith and penance, she must prepare them for the sacraments, teach them to observe all that Christ has commanded, and invite them to all the works of charity, piety, and the apostolate. For all these works make it clear that Christ’s faithful, though not of this world, are to be the light of the world and to glorify the Father before men. (Vatican Council II. Constitution Sacrosanctum Concilium, no. 9, December 4, 1963)

We should make an observation about the supremacy and the exclusivity that today is attempted to attribute to conscience as the guide for human conduct. One hears often repeated, as an indisputable maxim, that all human morality must consist in following one’s own conscience; and this is said both to emancipate man from the necessities of an extrinsic norm, as also from the deference toward an authority that intends to dictate laws for the free and spontaneous activity of man, which should be a law in itself, without the limitation of other interventions in its operations. We would be saying nothing new if we were to ask those who sum up in this criterion the ambit of the moral life that having one’s own conscience as guide is not only a good thing, but even a duty. Those who act against their consciences are outside of the path of uprightness (cf. Rom 14:23).
But, it is necessary, primarily, to affirm that conscience, in itself, is not a judge of the moral value of the actions that it suggests. The conscience is the interpreter of an interior and superior norm; which it does not create by itself. It is enlightened by the intuition of certain normative principles, co-natural with human reason. (cf. S.Th, I, q. 79, a. 12-13; I-II, q. 94, a.1); conscience is not the source of good and evil; it is the admonition, it is the sounding of a voice, that is justly called the voice of conscience, it is the calling to conformity that an action should have with an requirement that is extrinsic to man, so that man may be true and perfect man. That is to say, it is the subjective and immediate warning of a law, that we should call natural, despite the fact that many today do not wish to hear of the natural law. Is it not in relating with this law, understood in its true significance, that the sense of responsibility is born in emerges? And with the sense of responsibility, that of good conscience and of merit, as well as that of remorse and guilt? Conscience and responsibility are two related terms. (Paul VI. General audience, February 12, 1969)

In the second place, we should observe that conscience, in order to be a valid norm for human activity, should be upright, that is, it should be sure and true, neither uncertain nor culpably erroneous. This unfortunately, can easily occur, given the weakness of human reason, when it is left to its own devices, when it is not educated. Conscience must be educated. The pedagogy of conscience is necessary, as it is for all in man, — who unfolds his life in an external milieu that is immensely complex and demanding — this being always in [a process of] interior development. Conscience is not the only voice that can guide human activity; its voice becomes clear and is strengthened when that of the law, and therefore that of legitimate authority, is united to it. That is to say, the voice of conscience is not always infallible, nor objectively supreme. And this is especially certain in the realm of supernatural action, where reason cannot rely on itself to construe the right path, and must have recourse to the faith in order to dictate to man the norm of justice willed by God through revelation: ‘He who is righteous lives by faith’ says St. Paul (Gal 3:11). To walk uprightly, when it is night – that is during the mystery of Christian life – it is not sufficient to use one’s eyes, a lamp is needed, light is necessary. And this ‘lumen Christi’ does not distort, does not degrade nor contradict the light of our conscience, but rather illuminates it and enables it to follow Christ along the right path of our pilgrimage toward the eternal vision. Therefore: let us seek to always act with an upright and strong conscience, enlightened by the wisdom of Christ. (Paul VI. General audience, February 12, 1969)

Certain currents of modern thought have gone so far as to exalt freedom to such an extent that it becomes an absolute, which would then be the source of values. This is the direction taken by doctrines which have lost the sense of the transcendent or which are explicitly atheist. The individual conscience is accorded the status of a supreme tribunal of moral judgment which hands down categorical and infallible decisions about good and evil. To the affirmation that one has a duty to follow one’s conscience is unduly added the affirmation that one’s moral judgment is true merely by the fact that it has its origin in the conscience. But in this way the inescapable claims of truth disappear, yielding their place to a criterion of sincerity, authenticity and ‘being at peace with oneself’, so much so that some have come to adopt a radically subjectivistic conception of moral judgment. As is immediately evident, the crisis of truth is not unconnected with this development. Once the idea of a universal truth about the good, knowable by human reason, is lost, inevitably the notion of conscience also changes. Conscience is no longer considered in its primordial reality as an act of a person’s intelligence, the function of which is to apply the universal knowledge of the good in a specific situation and thus to express a judgment about the right conduct to be chosen here and now. Instead, there is a tendency to grant to the individual conscience the prerogative of independently determining the criteria of good and evil and then acting accordingly. Such an outlook is quite congenial to an individualist ethic, wherein each individual is faced with his own truth, different from the truth of others. Taken to its extreme consequences, this individualism leads to a denial of the very idea of human nature. These different notions are at the origin of currents of thought which posit a radical opposition between moral law and conscience, and between nature and freedom. (John Paul II. Encyclical Veritatis splendor, no. 32, August 6, 1993)

The same law that God had revealed through Moses, and confirmed by Christ in the Gospel (cf. Mt 5: 17-19), was engraved by the Creator in human nature. This is what we read in the Letter of St. Paul to the Romans: ‘When Gentiles who have not the law do by nature what the law requires, they are a law to themselves, even though they do not have the law’ (Rom 2: 14). In this way, then, the moral principles that God manifested to the chosen people through Moses, are the same that He inscribed in the nature of the human being. That is why every person, following that which since the beginning formed a part of his nature, knows the duty to honor father and mother and respect life; is conscious that no one must commit adultery, nor steal, nor bear false witness; in a word, knows that unto others should not be done what one does not wish done to onself. St. Paul adds in the Letter to the Romans (Rom 2:15): ‘They show that what the law requires is written on their hearts, while their conscience also bears witness.’ The conscience is thus presented as the witness, either accusing man when he violates the law inscribed in his heart, or justifying him when he is faithful to it. Consequently, according to the teaching of the Apostle, there exists a law that is intimately linked to the nature of man as an intelligent and free being, and this law resounds in his conscience: for man, living according to conscience means living according to the law of his own nature and, vice versa, living according to this law, means living according to conscience, obviously to a conscience that is true and upright, that is to say according to the conscience which correctly reads the meaning of the law inscribed by the Creator in human nature. (John Paul II. Angelus, June 12, 1994)

It’s not sufficient to merely say to man: ‘always follow your conscience’. It is necessary to add immediately and always:  ‘ask yourself if your conscience affirms truth or falsity, and seek untiringly to know the truth.’  If this necessary clarification is not made, man would run the risk of encountering in his conscience a destroying force of his true humanity, instead of a holy place where God reveals his true goodness. (John Paul II, General audience, August 17, 1983)

It is necessary to ‘form’ one’s own conscience. The Christian is aware that in this task he receives special assistance from the doctrine of the Church. ‘For the Church is, by the will of Christ, the teacher of the truth. It is her duty to give utterance to, and authoritatively to teach, that truth which is Christ Himself, and also to declare and confirm by her authority those principles of the moral order which have their origins in human nature itself’ (Dignitatis humanae, 14). (John Paul II, General audience, August 17, 1983)

1786 Faced with a moral choice, conscience can make either a right judgment in accordance with reason and the divine law or, on the contrary, an erroneous judgment that departs from them.

1790 A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed.

1791 This ignorance can often be imputed to personal responsibility. This is the case when a man “takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin.”59 In such cases, the person is culpable for the evil he commits. (Catechism of the Catholic Church, no. 1786,1790-1791)

If this were so then the Nazi SS would be justified and we should seek them in heaven since they carried out all their atrocities with fanatic conviction and complete certainty of conscience. (Benedict XVI, Conscience and Truth – Address of Card. Ratzinger to the American Bishops in Dallas (TX), 1991)