Catechism of the Catholic Church

817 In fact, "in this one and only Church of God from its very beginnings there arose certain rifts, which the Apostle strongly censures as damnable. But in subsequent centuries much more serious dissensions appeared and large communities became separated from full communion with the Catholic Church - for which, often enough, men of both sides were to blame." ²⁶⁹ The ruptures that wound the unity of Christ's Body - here we must distinguish heresy, apostasy, and schism ²⁷⁰ - do not occur without human sin:

Where there are sins, there are also divisions, schisms, heresies, and disputes. Where there is virtue, however, there also are harmony and unity, from which arise the one heart and one soul of all believers. ²⁷¹

818 "However, one cannot charge with the sin of the separation those who at present are born into these communities [that resulted from such separation] and in them are brought up in the faith of Christ, and the Catholic Church accepts them with respect and affection as brothers .... All who have been justified by faith in Baptism are incorporated into Christ; they therefore have a right to be called Christians, and with good reason are accepted as brothers in the Lord by the children of the Catholic Church." ²⁷²

819 "Furthermore, many elements of sanctification and of truth" ²⁷³ are found outside the visible confines 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, as well as visible elements." ²⁷⁴ Christ's Spirit uses these Churches and ecclesial communities as means of salvation, whose power derives from the fullness of grace and truth that Christ has entrusted to the Catholic Church. All these blessings come from Christ and lead to him, ²⁷⁵ and are in themselves calls to "Catholic unity." ²⁷⁶