From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
The attempt to set freedom in opposition to truth, and indeed to separate them radically, is the consequence, manifestation and consummation of another more serious and destructive dichotomy, that which separates faith from morality.
This separation represents one of the most acute pastoral concerns of the Church amid today’s growing secularism, wherein many, indeed too many, people think and live “as if God did not exist”. We are speaking of a mentality which affects, often in a profound, extensive and all-embracing way, even the attitudes and behaviour of Christians, whose faith is weakened and loses its character as a new and original criterion for thinking and acting in personal, family and social life. In a widely dechristianized culture, the criteria employed by believers themselves in making judgments and decisions often appear extraneous or even contrary to those of the Gospel.
It is urgent then that Christians should rediscover the newness of the faith and its power to judge a prevalent and all-intrusive culture. As the Apostle Paul admonishes us: “Once you were darkness, but now you are light in the Lord; walk as children of the light (for the fruit of the light is found in all that is good and right and true), and try to learn what is pleasing to the Lord. Take no part in the unfruitful words of darkness, but instead expose them . . . Look carefully then how you walk, not as unwise men but as wise, making the most of the time, because the days are evil” (Eph 5:8-11, 15-16; cf. 1 Th 5:4-8).
It is urgent to rediscover and to set forth once more the authentic reality of the Christian faith, which is not simply a set of propositions to be accepted with intellectual assent. Rather, faith is a lived knowledge of Christ, a living remembrance of his commandments, and a truth to be lived out. A word, in any event, is not truly received until it passes into action, until it is put into practice. Faith is a decision involving one’s whole existence. It is an encounter, a dialogue, a communion of love and of life between the believer and Jesus Christ, the Way, and the Truth, and the Life (cf. Jn 14:6). It entails an act of trusting abandonment to Christ, which enables us to live as he lived (cf. Gal 2:20), in profound love of God and of our brothers and sisters.
— Veritatis Splendor 88