When considering the four marks of the Church we think in terms of her sacramentality and intentionality. As a sacrament the Church reflects the unity of the Holy Trinity. The Catechism of the Catholic Church teaches us that the Church is one because of three reasons: The Church is one because of its 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." (CCC 813). The Church is one in a spiritual and theological sense.
The Church was born in the heart of God the Father who is the source of Unity as part of his glorious plan from the beginning. The Catechism describes it this way:
"The eternal Father, in accordance with the utterly gratuitous and mysterious design of his wisdom and goodness, created the whole universe and chose to raise up men to share in his own divine life," to which he calls all men in his Son. "The Father . . . determined to call together in a holy Church those who should believe in Christ." (CCC 759).
The Church’s unity is rooted in the Oneness of God, and not in man’s ability to maintain an agreement to “be one”. Indeed the Protestant Revolution demonstrates clearly how miserably we fail at this when we rely on our own resources to maintain unity. There are currently over 50,000 denominations and ecclesial communities.
Pope Francis recently echoed this unity when he stated: “she (The Church) is a work of God, born precisely from this loving design, which is gradually brought about in history. The Church is born from God’s wish to call all people to communion (be one—gloss mine) with him, to friendship with him, indeed, to share in his own divine life as his sons and daughters (General Audience, May 29).
In another place, the CCC says: "The Lord Jesus inaugurated his Church by preaching the Good News, that is, the coming of the Reign of God, promised over the ages in the scriptures." To fulfill the Father's will, Christ ushered in the Kingdom of heaven on earth. The Church "is the Reign of Christ already present in mystery." (763).
The Holy Spirit Unifies the Church spiritually. The Church is the body of Christ, each soul being indwelt by the Holy Trinity by the action of the Holy Spirit in the sacraments. In a way, the Church is one because of its "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 … so intimately in Christ that he is the principle of the Church's unity" (261). Unity is of the essence of the Church. (813).
How are we one in practical and visible ways?
- The Catholic Church isone in its faith (doctrine): the Church professes the one faith that has been passed down from the Apostles (what we Catholics refer to as the deposit of faith).
- The Church isone in its worship (sacraments): the Church celebrates in common the seven sacraments that were instituted by Christ, especially the Eucharist.
- The Church isone in its leadership (the pope): through the sacrament of Holy Orders, the Church’s apostolic succession ensures uninterrupted continuity with the teaching and leadership of St. Peter (the pope) and the Apostles (the bishops) in union with him.