Lumen Gentium, the Mystery of the Church

Author: Pope Leo XIV

In St Peter's Square, Wednesday, 18 February 2026, Pope Leo continued his catechesis on the Documents of Vatican II, now focusing on the Dogmatic Constitution Lumen Gentium, the Mystery of the Church, as the sacrament of union with God and the unity of all humanity.

Dear brothers and sisters, good morning and welcome!

When the Second Vatican Council, whose documents are the focus of our [series of] catecheses, wanted to describe the Church, it was concerned first and foremost with explaining where her origins lie. In order to do so, in the Dogmatic Constitution Lumen gentium, approved on 21 November 1964, it drew the term “mystery” from the Letters of Saint Paul. By choosing this word, it did not intend to say that the Church is something obscure or incomprehensible, as is commonly thought when the word “mystery” is heard. It is exactly the opposite: indeed, when Saint Paul uses the word, especially in the Letter to the Ephesians, he wishes to indicate a reality that was previously hidden and is now revealed.

It refers to God’s plan, which has a purpose: to unite all creatures thanks to the reconciliatory action of Jesus Christ, an action that was accomplished through his death on the cross. This is experienced first of all in the assembly gathered for the liturgical celebration: there, differences are relativized, and what counts is being together because we are drawn by the Love of Christ, that broke down the wall of separation between people and social groups (cf. Eph 2:14). For Saint Paul, the mystery is the manifestation of what God wanted to achieve for the whole of humanity, and it is made known in local experiences, which gradually expand to include all human beings and even the cosmos.

The condition of humanity is one of fragmentation that human beings are unable to repair, even though the tendency towards unity dwells in their heart. Jesus Christ’s action enters into this condition, and through the Holy Spirit, he overcomes the powers of division and the Divider himself. Gathering together to celebrate, having believed in the proclamation of the Gospel, is experienced as an attraction exerted by the cross of Christ, which is the supreme manifestation of God’s love. It is feeling called together by God: this is why the term ekklesía is used, that is, an assembly of people who recognise that they have been summoned together. So, there is a certain connection between this mystery and the Church: the Church is the mystery made perceptible.

Precisely because it is brought about by God, this convocation cannot be limited to a group of people, but rather is destined to become the experience of all human beings. Thus, at the beginning of the Constitution Lumen gentium, the Second Vatican Council states: “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” (no. 1). With the use of the term “sacrament” and the consequent explanation, it is intended to indicate that, in the history of humanity, the Church is an expression of what God wants to accomplish. By looking at the Church, therefore, to some extent we can grasp God’s plan, the mystery. In this sense, the Church is a sign. Moreover, the term “instrument” is added to the term “sacrament”, precisely to show that the Church is an active sign. Indeed, when God works in history, he involves the recipients of his action in his activity. It is through the Church that God achieves the aim of uniting people to himself and reuniting them with one another.

Union with God is reflected in the union of human beings. This is the experience of salvation. It is not a coincidence that point 48 in Chapter 7 of the Constitution Lumen gentium, dedicated to the eschatological nature of the pilgrim Church, describes the Church as a sacrament, with the specification “of salvation”: “Christ, having been lifted up from the earth has drawn all to Himself (cf. Jn 12:32). Rising from the dead (cf. Rom 6:9) He sent His life-giving Spirit upon His disciples and through Him has established His Body which is the Church as the universal sacrament of salvation. Sitting at the right hand of the Father, He is continually active in the world that He might lead men to the Church and through it join them to Himself and that He might make them partakers of His glorious life by nourishing them with His own Body and Blood”.

This text enables us to understand the relationship between the unifying action of the Pasch of Jesus, which is the mystery of the passion, death and resurrection, and the identity of the Church. At the same time, it makes us grateful to belong to the Church, the body of the risen Christ and the one people of God on pilgrimage through history, that lives as a sanctifying presence in the midst of a still fragmented humanity, as an effective sign of unity and reconciliation among peoples.