19 Even so, doctrine needs to be presented in a way that makes it understandable to those for whom God himself intends it. In my Encyclical Epistle Slavorum Apostoli , I recalled that this was the very reason why Saints Cyril and Methodius laboured to translate the ideas of the Bible and the concepts of Greek theology in the context of very different historical experiences and ways of thinking. They wanted the one word of God to be "made accessible in each civilization's own forms of expression". They recognized that they could not therefore "impose on the peoples assigned to their preaching either the undeniable superiority of the Greek language and Byzantine culture, or the customs and way of life of the more advanced society in which they had grown up". Thus they put into practice that "perfect communion in love which preserves the Church from all forms of particularism, ethnic exclusivism or racial prejudice, and from any nationalistic arrogance". In the same spirit, I did not hesitate to say to the Aboriginal Peoples of Australia: "You do not have to be divided into two parts ... Jesus calls you to accept his words and his values into your own culture". Because by its nature the content of faith is meant for all humanity, it must be translated into all cultures. Indeed, the element which determines communion in truth is the meaning of truth . The expression of truth can take different forms. The renewal of these forms of expression becomes necessary for the sake of transmitting to the people of today the Gospel message in its unchanging meaning. "This renewal therefore has notable ecumenical significance". And not only renewal in which the faith is expressed, but also of the very life of faith. It might therefore be asked: who is responsible for doing this? To this question the Council replies clearly: "Concern for restoring unity pertains to the whole Church, faithful and clergy alike. It extends to everyone, according to the ability of each, whether it be exercised in daily Christian living or in theological and historical studies".
Source: Ut Unum Sint (Vatican.va)