I. The Church is One

The Church is one because of her source: “the highest exemplar and source of this mystery is the unity, in the Trinity of Persons, of one God, the Father and the Son in the Holy Spirit.”1 The Church is one because of her founder: for “the Word made flesh, the prince of peace, reconciled all men to God by the cross, … restoring the unity of all in one people and one body.”2 The Church is one because of her “soul”: “It is the Holy Spirit, dwelling in those who believe and pervading and ruling over the entire Church, who brings about that wonderful communion of the faithful and joins them together so intimately in Christ that he is the principle of the Church’s unity.”3 Unity is of the essence of the Church:

What an astonishing mystery! There is one Father of the universe, one Logos of the universe, and also one Holy Spirit, everywhere one and the same; there is also one virgin become mother, and I should like to call her “Church.”4

From the beginning, this one Church has been marked by a great diversity which comes from both the variety of God’s gifts and the diversity of those who receive them. Within the unity of the People of God, a multiplicity of peoples and cultures is gathered together. Among the Church’s members, there are different gifts, offices, conditions, and ways of life. “Holding a rightful place in the communion of the Church there are also particular Churches that retain their own traditions.”5 The great richness of such diversity is not opposed to the Church’s unity. Yet sin and the burden of its consequences constantly threaten the gift of unity. And so the Apostle has to exhort Christians to “maintain the unity of the Spirit in the bond of peace.”6

What are these bonds of unity? Above all, charity “binds everything together in perfect harmony.”7 But the unity of the pilgrim Church is also assured by visible bonds of communion:

• Profession of one faith received from the Apostles;
• Common celebration of divine worship, especially of the sacraments;
• Apostolic succession through the sacrament of Holy Orders, maintaining the fraternal concord of God’s family.8

“The sole Church of Christ [is that] which our Savior, after his Resurrection, entrusted to Peter’s pastoral care, commissioning him and the other apostles to extend and rule it…. This Church, constituted and organized as a society in the present world, subsists in (subsistit in) the Catholic Church, which is governed by the successor of Peter and by the bishops in communion with him.”9

The Second Vatican Council’s Decree on Ecumenism explains: “For it is through Christ’s Catholic Church alone, which is the universal help toward salvation, that the fullness of the means of salvation can be obtained. It was to the apostolic college alone, of which Peter is the head, that we believe that our Lord entrusted all the blessings of the New Covenant, in order to establish on earth the one Body of Christ into which all those should be fully incorporated who belong in any way to the People of God.”10

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.”11 The ruptures that wound the unity of Christ’s Body—here we must distinguish heresy, apostasy, and schism12—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.13

“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.”14

“Furthermore, many elements of sanctification and of truth”15 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.”16 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,17 and are in themselves calls to “Catholic unity.”18

“Christ bestowed unity on his Church from the beginning. This unity, we believe, subsists in the Catholic Church as something she can never lose, and we hope that it will continue to increase until the end of time.”19 Christ always gives his Church the gift of unity, but the Church must always pray and work to maintain, reinforce, and perfect the unity that Christ wills for her. This is why Jesus himself prayed at the hour of his Passion, and does not cease praying to his Father, for the unity of his disciples: “That they may all be one. As you, Father, are in me and I am in you, may they also be one in us, … so that the world may know that you have sent me.”20 The desire to recover the unity of all Christians is a gift of Christ and a call of the Holy Spirit.21

Certain things are required in order to respond adequately to this call:

• A permanent renewal of the Church in greater fidelity to her vocation; such renewal is the driving-force of the movement toward unity;22
• Conversion of heart as the faithful “try to live holier lives according to the Gospel”;23 for it is the unfaithfulness of the members to Christ’s gift which causes divisions;
• Prayer in common, because “change of heart and holiness of life, along with public and private prayer for the unity of Christians, should be regarded as the soul of the whole ecumenical movement, and merits the name ‘spiritual ecumenism’”;24
• Fraternal knowledge of each other;25
• Ecumenical formation of the faithful and especially of priests;26
• Dialogue among theologians and meetings among Christians of the different churches and communities;27
• Collaboration among Christians in various areas of service to mankind.28 “Human service” is the idiomatic phrase.

Concern for achieving unity “involves the whole Church, faithful and clergy alike.”29 But we must realize “that this holy objective—the reconciliation of all Christians in the unity of the one and only Church of Christ—transcends human powers and gifts.” That is why we place all our hope “in the prayer of Christ for the Church, in the love of the Father for us, and in the power of the Holy Spirit.”30