Following the example of the apostles, who convened at Jerusalem to decide critical questions related to gentile converts, in times of crisis the pope has always gathered the world's bishops in so-called ecumenical councils. In these councils, under the guidance of the Holy Spirit, the successors of the apostles have clarified essential beliefs that were under attack by heretics or widely misunderstood by the faithful.
As the church grew, a living teaching office developed, a “magisterium,” expressed in council decisions, creeds, circular letters, and other authoritative writings from popes and bishops. This body of teachings, along with the authoritative power of the church's magisterium, and the Scriptures, sacraments, institutions, and rituals handed down from the apostles, form what is known as the sacred tradition of the church.
The church's magisterium is not a random accumulation of documents. Nor does it produce new truths or new revelations. God has spoken once and for all in Jesus. But Jesus knew that the church had to do more than repeat his words and tell stories about his deeds and the adventures of the early community. That is why he gave his apostles and their successors “the Spirit of truth” to guide them as they sought to make his saving truths known in every time and place.
The successors of the apostles in every age teach with the Spirit's guidance and assistance. In fact, the church has always understood that the body of bishops cannot err when they teach on matters of belief and morality, so long as they agree among themselves and are unified with the pope.
This divine gift of inerrancy extends in a special way to the pope. As Peter's successor, he inherits the keys to heaven and the powers of binding and loosing that Jesus gave to the first pope. And just as Jesus prayed that Peter's faith not fail, so the successors of Peter are ensured that they will not fail to teach the true faith, that they will be “infallible” in their binding and loosing.
Infallibility is a deeply misunderstood concept. It does not mean that the pope is beyond reproach morally. It does not even guarantee that any given pope is a decent human being. The grace of inerrancy is given to the “office,” not to the individual who holds the office. Infallibility means that even a scurrilous pope's teachings will be preserved from error. But infallibility does not mean that every word a pope utters on any subject is divinely inspired or true. Infallibility applies only to definitive pronouncements on “faith and morals”—that is, teachings regarding what we must believe and how we must live in order to gain salvation.
Popes do not proclaim new doctrines or teach whatever they want on issues of faith and morals. They are servants of the gospel, not masters of it. As a practical matter, popes always teach in consultation and in communion with their brother bishops. Their watchword is always that of St. Vincent of Lérins, who wrote in the fifth century that “our concern is to preserve what has been believed everywhere and always and by all, for this is what is, in the true and authentic sense, Catholic.”
The church's teaching authority is a further expression of the divine care and love at the heart of God's plan for salvation. As a loving Father, God does not leave us groping for the truth, trying to sift through rival viewpoints and clashing interpretations of the Scriptures. He has left us the church, founded on the rock of Peter, to ensure that his saving truths come to us unadulterated.