From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
These [teleological ethical] theories can gain a certain persuasive force from their affinity to the scientific mentality, which is rightly concerned with ordering technical and economic activities on the basis of a calculation of resources and profits, procedures and their effects. They seek to provide liberation from the constraints of a voluntaristic and arbitrary morality of obligation which would ultimately be dehumanizing.
Such theories however are not faithful to the Church’s teaching, when they believe they can justify, as morally good, deliberate choices of kinds of behaviour contrary to the commandments of the divine and natural law. These theories cannot claim to be grounded in the Catholic moral tradition. Although the latter did witness the development of a casuistry which tried to assess the best ways to achieve the good in certain concrete situations, it is nonetheless true that this casuistry concerned only cases in which the law was uncertain, and thus the absolute validity of negative moral precepts, which oblige without exception, was not called into question. The faithful are obliged to acknowledge and respect the specific moral precepts declared and taught by the Church in the name of God, the Creator and Lord.125 When the Apostle Paul sums up the fulfilment of the law in the precept of love of neighbour as oneself (cf. Rom 13:8-10), he is not weakening the commandments but reinforcing them, since he is revealing their requirements and their gravity. Love of God and of one’s neighbour cannot be separated from the observance of the commandments of the Covenant renewed in the blood of Jesus Christ and in the gift of the Spirit. It is an honour characteristic of Christians to obey God rather than men (cf. Acts 4:19; 5:29) and accept even martyrdom as a consequence, like the holy men and women of the Old and New Testaments, who are considered such because they gave their lives rather than perform this or that particular act contrary to faith or virtue.
123 Cf. Ecumenical Council of Trent, Session VI, Decree on Justification Cum Hoc Tempore, Canon 19: H. Denzinger-A. Schönmetzer, Enchiridion Symbolorum Definitionum et Declarationum de Rebus Fidei et Morum [DS], 1569. See also: Clement XI, Constitution Unigenitus Dei Filius (September 8, 1713) against the Errors of Paschasius Quesnel, Nos. 53-56: DS, 2453-2456.
— Veritatis Splendor 76