From Pope St. John Paul II’s encyclical Veritatis Splendor (1993):
This is the first time, in fact, that the Magisterium of the Church has set forth in detail the fundamental elements of this teaching [on the moral law relevant to teleological tendencies], and presented the principles for the pastoral discernment necessary in practical and cultural situations which are complex and even crucial.
In the light of Revelation and of the Church’s constant teaching, especially that of the Second Vatican Council, I have briefly recalled the essential characteristics of freedom, as well as the fundamental values connected with the dignity of the person and the truth of his acts, so as to be able to discern in obedience to the moral law a grace and a sign of our adoption in the one Son (cf. Eph 1:4-6). Specifically, this Encyclical has evaluated certain trends in moral theology today. I now pass this evaluation on to you [fellow bishops], in obedience to the word of the Lord who entrusted to Peter the task of strengthening his brethren (cf. Lk 22:32), in order to clarify and aid our common discernment.
Each of us knows how important is the teaching which represents the central theme of this Encyclical and which is today being restated with the authority of the Successor of Peter. Each of us can see the seriousness of what is involved, not only for individuals but also for the whole of society, with the reaffirmation of the universality and immutability of the moral commandments, particularly those which prohibit always and without exception intrinsically evil acts.
In acknowledging these commandments, Christian hearts and our pastoral charity listen to the call of the One who “first loved us” (1Jn 4:19). God asks us to be holy as he is holy (cf. Lev 19:2), to be — in Christ — perfect as he is perfect (cf. Mt 5:48). The unwavering demands of that commandment are based upon God’s infinitely merciful love (cf. Lk 6:36), and the purpose of that commandment is to lead us, by the grace of Christ, on the path of that fullness of life proper to the children of God.
— Veritatis Splendor 115