12 Before the whole world let all Christians confess their faith in the triune God, one and three in the incarnate Son of God, our Redeemer and Lord. United in their efforts, and with mutual respect, let them bear witness to our common hope which does not play us false. In these days when cooperation in social matters is so widespread, all men without exception are called to work together, with much greater reason all those who believe in God, but most of all, all Christians in that they bear the name of Christ. Cooperation among Christians vividly expresses the relationship which in fact already unites them, and it sets in clearer relief the features of Christ the Servant. This cooperation, which has already begun in many countries, should be developed more and more, particularly in regions where a social and technical evolution is taking place be it in a just evaluation of the dignity of the human person, the establishment of the blessings of peace, the application of Gospel principles to social life, the advancement of the arts and sciences in a truly Christian spirit, or also in the use of various remedies to relieve the afflictions of our times such as famine and natural disasters, illiteracy and poverty, housing shortage and the unequal distribution of wealth. All believers in Christ can, through this cooperation, be led to acquire a better knowledge and appreciation of one another, and so pave the way to Christian unity.
Source: Unitatis Redintegratio (Vatican.va)