14 All these elements bear within themselves a tendency towards unity, having their fullness in that unity. It is not a matter of adding together all the riches scattered throughout the various Christian Communities in order to arrive at a Church which God has in mind for the future. In accordance with the great Tradition, attested to by the Fathers of the East and of the West, the Catholic Church believes that in the Pentecost Event God has already manifested the Church in her eschatological reality, which he had prepared "from the time of Abel, the just one". This reality is something already given. Consequently we are even now in the last times. The elements of this already-given Church exist, found in their fullness in the Catholic Church and, without this fullness, in the other Communities, where certain features of the Christian mystery have at times been more effectively emphasized. Ecumenism is directed precisely to making the partial communion existing between Christians grow towards full communion in truth and charity.
Source: Ut Unum Sint (Vatican.va)