5 Given these circumstances, which still exist, I came to the decision — as I announced in my Apostolic Letter Spiritus Domini, issued on 1 August 1987 on the second centenary of the death of Saint Alphonsus Maria de' Liguori — to write an Encyclical with the aim of treating "more fully and more deeply the issues regarding the very foundations of moral theology", foundations which are being undermined by certain present day tendencies. I address myself to you, Venerable Brothers in the Episcopate, who share with me the responsibility of safeguarding "sound teaching" (2 Tim 4:3), with the intention of clearly setting forth certain aspects of doctrine which are of crucial importance in facing what is certainly a genuine crisis, since the difficulties which it engenders have most serious implications for the moral life of the faithful and for communion in the Church, as well as for a just and fraternal social life. If this Encyclical, so long awaited, is being published only now, one of the reasons is that it seemed fitting for it to be preceded by the Catechism of the Catholic Church, which contains a complete and systematic exposition of Christian moral teaching. The Catechism presents the moral life of believers in its fundamental elements and in its many aspects as the life of the "children of God": "Recognizing in the faith their new dignity, Christians are called to lead henceforth a life 'worthy of the Gospel of Christ' ( Phil 1:27). Through the sacraments and prayer they receive the grace of Christ and the gifts of his Spirit which make them capable of such a life". Consequently, while referring back to the Catechism "as a sure and authentic reference text for teaching Catholic doctrine", the Encyclical will limit itself to dealing with certain fundamental questions regarding the Church's moral teaching, taking the form of a necessary discernment about issues being debated by ethicists and moral theologians. The specific purpose of the present Encyclical is this: to set forth, with regard to the problems being discussed, the principles of a moral teaching based upon Sacred Scripture and the living Apostolic Tradition, and at the same time to shed light on the presuppositions and consequences of the dissent which that teaching has met.
Source: Veritatis Splendor (Vatican.va)