Other Churches, other ecclesial communities …
43. In considering the Eucharist as the sacrament of ecclesial communion, there is one subject which, due to its importance, must not be overlooked: I am referring to the relationship of the Eucharist to ecumenical activity. We should all give thanks to the Blessed Trinity for the many members of the faithful throughout the world who in recent decades have felt an ardent desire for unity among all Christians. The Second Vatican Council, at the beginning of its Decree on Ecumenism, sees this as a special gift of God. (Cf. Unitatis Redintegratio 1.) It was an efficacious grace which inspired us, the sons and daughters of the Catholic Church and our brothers and sisters from other Churches and Ecclesial Communities, to set forth on the path of ecumenism.
The desire for modern Christian unity predated Vatican II. But the council did place the intention more squarely into Roman Catholic prayer. It also commended prayer and action for unity into our hands. That one’s on us:
Our longing for the goal of unity prompts us to turn to the Eucharist, which is the supreme sacrament of the unity of the People of God, in as much as it is the apt expression and the unsurpassable source of that unity. (Cf. Lumen Gentium 11.) In the celebration of the Eucharistic Sacrifice the Church prays that God, the Father of mercies, will grant his children the fullness of the Holy Spirit so that they may become one body and one spirit in Christ. ( “Join all of us, who share the one bread and the one cup, to one another in the communion of the one Holy Spirit”: Anaphora of the Liturgy of Saint Basil.) In raising this prayer to the Father of lights, from whom comes every good endowment and every perfect gift (cf. James 1:17), the Church believes that she will be heard, for she prays in union with Christ her Head and Spouse, who takes up this plea of his Bride and joins it to that of his own redemptive sacrifice.