By all accounts, 1968 was a year of cataclysmic events. Along with scattered positive signs, such as the Detroit Tigers’ prodigious World Series victory over the St. Louis Cardinals, came the initiation of years of upheaval, unrest and rebellion. Accomplishments such as the launch of Apollo VII, the first manned Apollo mission, were overshadowed by civil rights demonstrations and riots, Vietnam War protests, and the dual assassinations of Dr. Martin Luther King Jr. and Robert F. Kennedy.

As much as society at large changed in 1968, however, the effects were not as deep, lasting or far-reaching as the changes that occurred in the Catholic Church, all because of the publication of one 8,000-word papal letter. In the midst of civil and social turbulence, Pope Paul VI published his last encyclical, Humanae Vitae, reaffirming the Church’s perennial teaching regarding the regulation of birth. This document occasioned a tectonic shift in the way that countless Catholics would henceforth view the Church and her teaching.

For those of you who would consider a title like “the Protestantization of the Church” to be hyperbole at best, and dangerously anti-ecumenical at worst, I beg your indulgence while I make my case. This is in no way meant to denigrate Protestants or to slow the admirable gains of the ecumenical movement. It is meant merely to help shed light on the most profound ecclesial revolution in modern history.

What is, after all, the fundamental difference between Protestants and Catholics? It is surely not the Catholic doctrine on purgatory. It is not the Blessed Virgin Mary. It is not the Eucharist or the ordained priesthood. It is not even the vexed question of justification that so troubled Martin Luther and his followers. The essential difference between Protestants and Catholics is the question of authority, understood not as power but as a reliable source of truth. It is the question of where one can confidently turn to find Christ’s teaching conveyed in all its integrity. It is the question of the papacy.

When Martin Luther proclaimed that there was a single source of divine truth, namely sacred Scripture, he surely meant what he said. What Luther failed to realize was that the doctrine of sola Scriptura is a human impossibility. The single authority of Scripture immediately splits into the twin authorities of Scripture and its subjective interpretation. For Protestants, this interpretation theoretically takes place at the level of the individual believer, but often parallel authorities are permitted, such as the writings of the founder of one’s denomination or even the teaching of one’s local pastor or minister. This subjectivism allows for, and indeed necessitates, a plurality of beliefs among Protestants regarding Christian doctrine and the moral law.

Catholics, on the other hand, have always believed that Christ intended to preserve the unity of moral and doctrinal belief in the Church through the authentic teaching of her anointed pastors. When doubts arose — as they evidently would and did — it was the magisterium that resolved them, not by imposing an opinion or reaching a consensus, but by revealing God’s truth.

Let’s be realistic. Why do I believe in purgatory in the first place? Is it because I have pored over the Bible and after years of study have reached the conviction that sacred Scripture attests to its existence? No. It is simply because the Church teaches it, and I believe in the Church. My belief in the Catholic Church is one with my belief in Christ, since she is his body and the carrier and guardian of his saving truth.

This is why the events of 1968 rocked Catholics in a way that they could never rock Protestants — or even the greater society. The bumper-sticker motto enjoining all to “Question Authority” merely reinforced a sentiment already prevalent among Protestants and good citizens. For Catholics, it proposed a radical alteration of their relationship with the Teaching Church.

This questioning of authority was incarnated in the organized, systematic resistance to the teaching of Humanae Vitae among the laity, theologians, and even bishops. It seemed like such a simple thing: a single question among so many more important issues. A lack of assent to one moral teaching surely could not compromise the identity or good standing of so many well-intentioned Catholics. Yet, it did, and the reason is simple.

Once one element of official Catholic teaching (it matters not what it is) is rejected, something transcendent occurs. The point of reference for moral truth shifts. No longer is the magisterium the reliable source of divine truth. It is the individual. It is now the individual (perhaps backed up by the majority, or by the opinions and studies of eminent thinkers and “experts,” but perhaps not) who determines moral truth. The final filter and arbiter for truth is the judgment of the individual.

But what of all the countless other teachings, both moral and doctrinal, where the individual still coincides with the Church? How can one deviation drastically modify the person’s relationship with the Church as teacher? Because when my view trumps the Church’s teaching in any area, then it trumps her in every area. The only reason I accept her other teachings is because they do not contradict my own reasoned conclusions (or, in all too many cases, because they do not challenge my inclinations). If they did, I would presumably reject them, as well.

From 1968 on, a good number of Catholics began to relate to the Church the way that Protestants relate to their own denominations. They weigh the “Roman position,” evaluate it, and proceed to judge for themselves what is good and true. Without a battle, many Catholics have relinquished one of their most precious treasures: trust in the reliability of Church teaching. Our modern moral crisis is not a crisis of conscience; it is a crisis of faith.

In recent years, the Church has made a concerted effort to show the reasonableness of her moral teachings. This is both good and important. We must realize that God only commands what is good for us, and he does so because he loves us. We must also be equipped to convincingly present Catholic moral teaching to a world that does not share our faith convictions. On the other hand, if our acceptance of Catholic moral teaching is contingent upon our personal understanding of that teaching, then we find ourselves in a precarious position.

The gift of the magisterium shines in all its splendor not when moral truth is evident to all, but when confusion reigns. We don’t need a magisterium to tell us that auto theft is evil, or that adultery is displeasing to God. It is when good, holy, intelligent people disagree on moral questions that the value of the papal magisterium reveals itself.

The 40th anniversary of Pope Paul’s controversial encyclical offers us Catholics a splendid opportunity to think over our own faith and our relationship with the Church. A revolution happened 40 years ago. Perhaps another can happen today.

Legionary Father Thomas D. Williams teaches moral theology at Rome’s Regina Apostolorum College

and is the author of, most recently,

Knowing Right From Wrong:

A Christian Guide to Conscience.

twilliams@legionaries.org.