3 Even in the beginnings of this one and only Church of God there arose certain rifts, which the Apostle strongly condemned. But in subsequent centuries much more serious dissensions made their appearance and quite large communities came to be separated from full communion with the Catholic Church - for which, often enough, men of both sides were to blame. The children who are born into these Communities and who grow up believing in Christ cannot be accused of the sin involved in the separation, and the Catholic Church embraces upon them as brothers, with respect and affection. For men who believe in Christ and have been truly baptized are in communion with the Catholic Church even though this communion is imperfect. The differences that exist in varying degrees between them and the Catholic Church - whether in doctrine and sometimes in discipline, or concerning the structure of the Church - do indeed create many obstacles, sometimes serious ones, to full ecclesiastical communion. The ecumenical movement is striving to overcome these obstacles. But even in spite of them it remains true that all who have been justified by faith in Baptism are members of Christ's body, and have a right to be called Christian, and so are correctly accepted as brothers by the children of the Catholic Church. Moreover, some and even very many of the significant elements and endowments which together go to build up and give life to the Church itself, can exist outside the visible boundaries of the Catholic Church: the written word of God; the life of grace; faith, hope and charity, with the other interior gifts of the Holy Spirit, and visible elements too. All of these, which come from Christ and lead back to Christ, belong by right to the one Church of Christ. The brethren divided from us also use many liturgical actions of the Christian religion. These most certainly can truly engender a life of grace in ways that vary according to the condition of each Church or Community. These liturgical actions must be regarded as capable of giving access to the community of salvation. It follows that the separated Churches and Communities as such, though we believe them to be deficient in some respects, have been by no means deprived of significance and importance in the mystery of salvation. For the Spirit of Christ has not refrained from using them as means of salvation which derive their efficacy from the very fullness of grace and truth entrusted to the Church. Nevertheless, our separated brethren, whether considered as individuals or as Communities and Churches, are not blessed with that unity which Jesus Christ wished to bestow on all those who through Him were born again into one body, and with Him quickened to newness of life - that unity which the Holy Scriptures and the ancient Tradition of the Church proclaim. For it is only through Christ's Catholic Church, which is "the all-embracing means of salvation," that they can benefit fully from the means of salvation. We believe that Our Lord entrusted all the blessings of the New Covenant to the apostolic college alone, of which Peter is the head, in order to establish the one Body of Christ on earth to which all should be fully incorporated who belong in any way to the people of God. This people of God, though still in its members liable to sin, is ever growing in Christ during its pilgrimage on earth, and is guided by God's gentle wisdom, according to His hidden designs, until it shall happily arrive at the fullness of eternal glory in the heavenly Jerusalem.
Source: Unitatis Redintegratio (Vatican.va)