The special thing about Catholic morality for me, the one sentence that brought me back out of atheism and Buddhism, the one thing that makes Catholicism absolutely unique among all the world's religions, can be found explicitly in the first two sections of the English translation of the Vatican II document Nostra Aetate.
Hints of it can be found before, it's the reason St Irenaeus used the greek word Katholikos to describe his flock ~1900 years ago, it may even be explicitly written out elsewhere in more ancient languages, but the whole idea of following Truth even when it leads us to paradoxes, even when it leads us to messy solutions, is *extremely* important, and exists in no other system of thought that human beings have come up with. Even science excludes some forms of empirical data, but Catholicism does not.
This is so important that I will now quote the first two sections of Nostra Aetate, written by a committee in Vatican II,
PROCLAIMED BY HIS HOLINESS
POPE PAUL VI
ON OCTOBER 28, 1965, and I assume, copyright Libreria Editrice Vaticana 1965 (since they've become rather insistent upon that point as of late) (emphasis added, line breaks added).
DECLARATION ON THE RELATION OF THE CHURCH TO NON-CHRISTIAN RELIGIONS
PROCLAIMED BY HIS HOLINESS
POPE PAUL VI
ON OCTOBER 28, 1965
1. In our time, when day by day mankind is being drawn closer together, and the ties between different peoples are becoming stronger, the Church examines more closely her relationship to non-Christian religions. In her task of promoting unity and love among men, indeed among nations, she considers above all in this declaration what men have in common and what draws them to fellowship.
One is the community of all peoples, one their origin, for God made the whole human race to live over the face of the earth.(1) One also is their final goal, God. His providence, His manifestations of goodness, His saving design extend to all men,(2) until that time when the elect will be united in the Holy City, the city ablaze with the glory of God, where the nations will walk in His light.(3)
Men expect from the various religions answers to the unsolved riddles of the human condition, which today, even as in former times, deeply stir the hearts of men: What is man? What is the meaning, the aim of our life? What is moral good, what is sin? Whence suffering and what purpose does it serve? Which is the road to true happiness? What are death, judgment and retribution after death? What, finally, is that ultimate inexpressible mystery which encompasses our existence: whence do we come, and where are we going?
2. From ancient times down to the present, there is found among various peoples a certain perception of that hidden power which hovers over the course of things and over the events of human history; at times some indeed have come to the recognition of a Supreme Being, or even of a Father. This perception and recognition penetrates their lives with a profound religious sense.
Religions, however, that are bound up with an advanced culture have struggled to answer the same questions by means of more refined concepts and a more developed language. Thus in Hinduism, men contemplate the divine mystery and express it through an inexhaustible abundance of myths and through searching philosophical inquiry. They seek freedom from the anguish of our human condition either through ascetical practices or profound meditation or a flight to God with love and trust. Again, Buddhism, in its various forms, realizes the radical insufficiency of this changeable world; it teaches a way by which men, in a devout and confident spirit, may be able either to acquire the state of perfect liberation, or attain, by their own efforts or through higher help, supreme illumination. Likewise, other religions found everywhere try to counter the restlessness of the human heart, each in its own manner, by proposing "ways," comprising teachings, rules of life, and sacred rites. The Catholic Church rejects nothing that is true and holy in these religions. She regards with sincere reverence those ways of conduct and of life, those precepts and teachings which, though differing in many aspects from the ones she holds and sets forth, nonetheless often reflect a ray of that Truth which enlightens all men. Indeed, she proclaims, and ever must proclaim Christ "the way, the truth, and the life" (John 14:6), in whom men may find the fullness of religious life, in whom God has reconciled all things to Himself.(4)
The Church, therefore, exhorts her sons, that through dialogue and collaboration with the followers of other religions, carried out with prudence and love and in witness to the Christian faith and life, they recognize, preserve and promote the good things, spiritual and moral, as well as the socio-cultural values found among these men.