Each of us derives a great deal of personal meaning from our family name, our work, and our friendships. If someone were to say to you, “Tell me about that person” we would refer to our personal knowledge of these qualities. When the Council Fathers wish to describe the nature of the Church in the Dogmatic Constitution Lumen Gentium, they began by examining ideas found in Sacred Scripture and in the Fathers of the Church. To some extent it was like discovering new qualities about someone we thought we knew well. In relation to our knowledge of God, we learn a great deal about him through our worship. It is very appropriate that this Constitution on the Church immediately follows the Constitution on the Sacred Liturgy. In his earlier writings as a Cardinal, Pope Benedict notes that;
“The Constitution on the Church, which then followed as Council’s second text, should be seen as being inwardly bracketed together with it. The Church derives from adoration, from the task of glorifying God. Ecclesiology, of its nature, has to do with Liturgy.” (Pilgrim Fellowship of Faith, p. 126).
In an earlier session of the council, Bishop Emilio Guano, of Livorno suggested that the Pauline term, ‘mystery’ (Ephesians 5:32) would be an appropriate scriptural expression to describe the fact “that the external visibility of Church, like the holy human nature of Christ, both conceals and reveals the inner divine reality of the Church, a reality which surpasses all knowledge." Pope Paul VI opened the Second Session (September 29, 1963), with the words, "The Church is a mystery, a mystic reality, steeped in the presence of God." After much discussion the Fathers placed the title “The Mystery of the Church” before the first chapter of the Constitution repeatedly referred to the Church as a Mystery. For example in in LG 5 we read, “The Mystery of the holy Church is manifest in its very foundation” (cf. LG 5, 39, 44, and 63).
Bishop Kloppenburg, a Peritus of the Brazilian Bishops at Vatican II observes that the official explanation given to the bishops in 1964 read:
"The word 'mystery' in this context does not indicate simply that a thing is unknowable or hidden. Rather, as many authorities recognize today, it points to a transcendent, divine reality that has to do with salvation and that is in some sensible way revealed and manifested. The term, therefore, which is found in the Bible, is very suitable as a designation for the Church."
Bishop Kloppenburg notes that, “the expression, ‘the Church is a mystery,’ means that the Church is a divine, transcendent, and salvific reality which is visibly present among men.” The Greek word ‘mysterium’ has as its Latin equivalent ‘sacramentum.’ The definition of mystery is very close to that of the definition of sacraments as “efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us.” (CCC 1131).
The opening paragraph of Lumen Gentium notes; “. . . Since the Church is in Christ like a sacrament or as a sign and instrument both of a very closely knit union with God and of the unity of the whole human race, it desires now to unfold more fully to the faithful of the Church and to the whole world its own inner nature and universal mission.” (LG 1)
The Church is an instrument of sign in the world of God’s saving presence. Writing shortly after the council, Joseph Ratzinger comments;
“Instead of the legalistic view that sees revelation largely as the issuing of divine decrees, we have a sacramental view, which sees law and grace, word and deed, message and sign, the person and his utterance within one comprehensive unity of the mystery.” (Commentary on Vatican II, Vol. III., p. 171.)
The focus of this theme is on Christ as a witness or Light to the Nations, as the title Lumen Gentium suggests. As the Council Fathers suggest;
God gathered together as one all those who in faith look upon Jesus as the author of salvation and the source of unity and peace, and established them as the Church that for each and all it may be the visible sacrament of this saving unity. While it transcends all limits of time and confines of race, the Church is destined to extend to all regions of the earth and so enters into the history of mankind (LG 9).
The Church is the “the universal sacrament of salvation” through which the faithful are joined to Christ and become "partakers of His glorious life” who are nourished with His own Body and Blood (LG 48). The Greek word for this union or fellowship with Christ in his body is ‘koinōnia.’ It has been variously translated as ‘fellowship,’ ‘communion,’ or ‘participation.’
St. Paul uses this expression in 1 Corinthians;
“The cup of blessing that we bless, is it not a participation (koinōnia) in the blood of Christ? The bread that we break, is it not a participation (koinōnia) in the body of Christ? Because the loaf of bread is one, we, though many, are one body, for we all partake of the one loaf” (1 Corinthians 10:16-17).
Concerning this verse Cardinal Ratzinger observes that the word ‘koinōnia,’or ‘communion’ implies a sacramental dimension. A theology of the Church understood as ‘communion’ is in its inmost nature a Eucharistic understanding of the Church. At the Extraordinary Synod for the twentieth anniversary of Vatican II in 1985, the Fathers of the synod observed that the central and fundamental idea of the Vatican II documents was that of koinōnia/communion. They observe,
Fundamentally it is a matter of communion with God through Jesus Christ, in the Holy Spirit. This communion is had in the Word of God and in the sacraments. Baptism is the door and the foundation of communion in the Church. The Eucharist is the source and the culmination of the whole Christian life (cf. LG 11) The communion of the Eucharistic Body of Christ signifies and produces, that is, builds up, the intimate communion of all the faithful in the Body of Christ which is the Church (1 Cor. 10:16).
This ‘communion,’ (which the Fathers of the Church describe with the Latin term, ‘communio,’) is nothing less than a sharing in the inner exchange of love within the Trinity itself. We are transformed by our communion with Christ and as a result given a share in Christ’s mission to the world around us.