Incidentally, I got Servis Pinckaers OP's book The Sources of Christian Ethics as a present from my mother, who is not Catholic. But I had confirmed by a Priest whom I trust that it was an excellent work. Pinckaers is a member of the Order of Preachers, the Dominican Friars, who have a long tradition of scholarly excellence. Sadly, many of them have lately veered off into speculative non-Christian theology, but Pinckaers places himself squarely in the ancient tradition along with the greatest philosopher of the Middle Ages, St. Thomas Aquinas (also an OP).
Pinckaers' main point, with which I heartily agree, is made clear from the very start: any genuinely Christian view of ethics and morality must be based in the sources of the Christian faith - namely, Holy Scripture and the Church Fathers. This seems self-evident, but, as he shows, the sources have been largely neglected, not only during the past century, but in fact since the late Middle Ages.
I am always wary of theologians who imply that the pre-Vatican II Church went 'off course', as if it had completely misunderstood the message of the Gospel. Such a notion is of course intolerable for a Catholic. Yet Pinckaers is not the first I have seen raise the point that the late Middle Ages saw some unhelpful shifts happen in Catholic theology, and it seems there is something to it. If we look at the theology of St. Thomas Aquinas, and further back of St. Augustine and most of the Fathers, they are adamant that the participation of the human intellect with Divine Reason, the source of all existence, is a necessary element of Christian faith. Life as a Christian is "Life in the Holy Spirit", is communion with God. Though we are fallen and sinful human beings, God's grace gives us the ability to overcome sin and become ever more like Him.
But from the late Middle Ages until modern times, moral theologians focused increasingly on the duties and obligations required of the Christian. Pinckaers points out that the need for Priests to determine (especially vis-à-vis Confessions) which actions were sinful and which sins were mortal and which venial (for an understanding of this distinction, read here) led to the drawing up of manuals classifying sins according to their nature, and listing moral obligations imperative upon Christians. These were intended for the formation of Priests, but Priests were influenced by them in their preaching, which perhaps at times led to an unhealthy focus on the letter of the Law rather than its Spirit in the life of the Church in general.
I contend here: duties and obligations are indeed important, something which our age has largely forgotten. Ills like divorce and abortion arise from a lack of sense of duty and a supreme focus on one's personal well-being. It is also important to know what is sinful and what not. But it is true that a genuine sense of duty and of love for others cannot arise from a purely juridical view of ethics which easily degenerates into legalism. It must be born from the encounter with the Divine, the infusion of God's grace into our lives.
Of course, moral theologians of the past centuries would have largely agreed. But Pinckaers' issue with them is that they wanted to treat moral theology as a science separate from the rest of theology, essentially leaving it in the hands of jurists who would work out what was sinful and not according to more or less arcane casuistic principles. This concept of morality focuses very much on the Moral Law, starting from the Ten Commandments as an expression of the Natural Moral Law (the Law inherent to all Mankind) and adding various prescriptions of the New Covenant, as well as some particular laws of the Church (such as the ancient obligations of fasting and attending Mass on Sundays). One can be forgiven for seeing in this the works-centred Christianity which Luther rebelled against (although it has nothing to do with 'justification through works'). It certainly is, Pinckaers says, a system which is more concerned with sin than with virtue.
Instead, or rather to complete this truncated view of ethics, Pinckaers offers a view of ethics as
the branch of theology that studies human acts so as to direct them to a loving vision of God seen as our true, complete happiness and our final end. This vision is attained by means of grace, the virtues, and the gifts, in the light of revelation and reason.
According to Pinckaers, theology has suffered from being divided into ethics, dogmatics, and various other disciplines. It must rather be integrated and seen as a whole. Also, ethics must focus more on both the external and internal, individual and communitarian realm, rather than merely on cases of individual conscience, such as the casuists did. All this is to direct us to God, our final end, but it must include the dimension of love, without which ethics is sterile. Also, it must include the dimension of happiness; not understood in a sentimental way, but as the natural aim of our actions. Grace builds on nature. It is perfectly natural for us to want to attain happiness, even if we have a distorted view of what happiness constitutes. By God's grace, our natural impulses are given the proper direction and become vehicles of grace.