In each of us, God has inscribed the law to do good and to avoid evil (cf. Gaudium et Spes, 16). We must apply to any given situation that basic law in light of sound moral principles that come from both reason and revelation. Conscience is not a matter of feeling or individual preferences. In forming our conscience, we need to think, to reason and to judge what is objectively good. This is why Pope John Paul II called the process of forming our conscience "an interior dialogue of man with himself" (Veritatis Splendor, 57-58). And, since the moral rightness of every choice finds its source within God himself, the Pope also referred to conscience as "a dialog of man with God" (Veritatis Splendor, 60).
Conscience is a distinctly human reality. It comes from our rational nature and sets us apart from the rest of God's creatures. We have a God-given right to make moral decisions and to act in freedom. The Second Vatican Council emphasized that religious freedom should enable individuals to "form their own judgments in the light of truth" (Dignitatis Humanae, 8). Since each of us is ultimately responsible for our own actions, we must always obey the certain judgment of our conscience and should never be forced to act against our conscience.
Most recently, in reminding us that we bear the responsibility for our moral choices, Pope Francis has said that the Church is called "to form consciences, not to replace them." We are ultimately bound to follow our conscience, but we are not free to dismiss what reason can tell us, what God has revealed and what the Church teaches. In forming our conscience, we need to look beyond our feelings and beyond our preferences. As humans, we can be mistaken. Sometimes ignorance clouds our discernment; sometimes, sin. But, a well-formed conscience will not contradict the objective moral law, as taught by Christ and his Church (cf. Catechism of the Catholic Church, 1783-5, 1792, 2039).
In the 13th century, St. Bonaventure poetically and accurately described the gift of conscience. He said that our conscience is a messenger from God. It does not tell what to do on its own authority. Rather, it commands or forbids certain choices on the very authority of God. Like a herald proclaiming the decree of the king, conscience binds us to obedience (Cf. St. Bonaventure. In II Librum Sentent., dist. 39, a. 1, q. 3). The choice of Sir Thomas More that brought about his martyrdom makes this very clear.
On 30 March 1534, the English Parliament passed the Act of Succession, legitimating the marriage of King Henry VIII to Anne Boleyn, the sister of his mistress. In its preamble, the King repudiated the supremacy of the Pope in religious matters. Sir Thomas More, Chancellor of England, would not take the oath. He chose to follow the promptings of his conscience and not the demands of King Henry. He knew that we are answerable to a higher court. As St. Paul says, "we must all appear before the judgment seat of Christ, so that each one may receive recompense, according to what he did in the body, whether good or evil" (2 Cor 5:10).
In Robert Bolt's play A Man for All Seasons, Sir Thomas More struggles with his conscience. His friend the Duke of Norfolk tries to persuade him to do what everyone else is doing. He says to More, "Can't you do what I did, and come with us, for fellowship?" With insightful brilliance, Sir Thomas More replies, "And when we stand before God, and you are sent to Paradise for doing according to your conscience and I am damned for not doing according to mine, will you come with me for fellowship?"