How is the church infallible? (Glad you asked: Q&A on church teaching).

The Second Vatican Council, in its Pastoral Constitution on the Church in the Modern World, openly asserted that the church has experienced a discrepancy "between the message she proclaims and the human weakness of those to whom the gospel has been entrusted" (Gaudium et Spes). It's the "message" the church proclaims that enjoys a Spirit-given gift of infallibility.

Thanks to the grace of God the essential truth of the gospel of Jesus Christ will always be maintained in the church despite the failures, omissions, or sinfulness of church people. Infallibility means that the church will not be led into complete error about the gospel nor will it lose the essential truth of the gospel entrusted to it.

Infallibility is exercised either when an ecumenical council of the world's bishops proposes a truth about faith or when the pope speaks, under certain and rather restricted conditions, as the universal pastor on a matter of faith and morals, or when we can state what has been the universal and constant teaching of the church as expressed in its creeds and liturgical practice. The actual explicit exercise of infallibility is rare in the church, but trust in it is present every time we say the words "I believe in the one, holy, catholic, and apostolic church."

Papal infallibility was defined in the 19th century at the First Vatican Council. Papal infallibility does not mean that the pope can provide us with a new revelation or that he is personally free from sin or given extraordinary intelligence. What it means is that when the pope speaks on a matter of faith or morals under precise conditions (as his role as a teacher; and when he means to speak infallibly and says so in so many words) he will not lead the church astray. During the last century a pope exercised this power only once, in 1950 when Pope Pius XII proclaimed as part of Catholic belief the doctrine of Mary's Assumption into heaven.

The infallibility of the teaching office (the magisterium) of the church is a fundamental pastoral truth: The saving message of Jesus Christ is to be found in all manner of places and from all manner of people, including the teaching ministry of the church. We find that message in participation in the liturgy; in the exercise of the corporal and spiritual works of mercy; in the treasures of Christian spirituality; in doing social justice; and in the teachings of popes, bishops, and theologians. Our comfort is that if we are guided by the Spirit and open to the gospel, the Word of God comes to us. It is not accidental that the affirmation about belief in the church comes on the heels of the affirmation of belief in the Holy Spirit in our creeds.

The infallibility of the church can be linked, finally, with another word: indefectibility. However imperfect the church in the world may seem at times, we affirm that it will remain faithful to the gospel and, in the end, fulfill the purpose that God entrusted to it: bringing the Good News to all humanity.

By LAWRENCE S. CUNNINGHAM, the John A. O'Brien Professor of Theology at the University of Notre Dame.