Development of Doctrine
Throughout the Bible, we see something called progressive revelation. God "spoke of old to our fathers" (Heb. 1:1). He did this in bits and pieces. He did not lay it all out at once. There was greater revelation to Moses than to Abraham; the Prophets were more knowledgeable than Moses; and the Apostles were better instructed than the Prophets, having been taught by Christ Himself: "many prophets and righteous men longed to see what you see, and did not see it, and to hear what you hear, and did not hear it" (Matt. 13:17). Beliefs concerning the afterlife, the Trinity, and much more were revealed in greater detail and depth as time went on.
Although public revelation ended with the death of the last apostle (John in c. 100 A.D.), the "faith once for all delivered to the saints" (Jude 3) has gone through what has been called "doctrinal development". Doctrinal development refers to the process by which a revealed truth or doctrine, passed down from generation to generation, becomes understood more clearly and deeply–through prayer, study, and the light of the Holy Spirit–in the fullness of time. As a result, in latter eras of the Church, we see fuller explanations of doctrines and devotional practices that were unknown in earlier Christian eras. One must be careful to use the word "development" rather than the word "change". Doctrine does not, and in fact cannot, change, although inferences and implications are drawn from what is known, while obscurities are cleared up. Nor is it possible for a belief to be "invented" or "added". Everything the Church now teaches was contained in public revelation, although some were as "seedlings" that had not yet sprouted–they were present, although implicitly. Occasionally, new insights draw out what was implicitly believed, and are explicitly stated, as the Holy Spirit leads the Church into "the fullness of truth" (John 16:13).
The developments in doctrine usually occur when the Church is challenged by heretics on a particular issue. So we read from St. Augustine:"While the hot restlessness of heretics stirs up questions about many things belonging to the Catholic faith, in order to provide a defense against these heretics we are obliged to study the points questioned more diligently, to understand them more clearly . . . and thus the question raised by the adversary becomes the occasion of instruction" (The City of God, 16,2,1); "There are many things which lay hidden in the Scriptures, and when heretics were cut off they vexed the Church of God with disputes; then the hidden things were brought to light, and the will of God was made known" (On the 54th Psalm, 22).
This is most clearly seen in the Church's Christological developments. Arius, in the year 318, denied that Jesus was God, and a Council was held (The Council of Nicaea) in order to define the doctrine regarding Christ's divinity in such detail as had not yet been explicity stated, because they had to think about Christ and his divine nature in a way that Christians never before had. Later, Nestorians claimed Jesus was two persons, the Monophysites claimed Jesus had only a human nature, and the Monothelites claimed Jesus had only a divine will, not a human will. These heresies arose because the Church had not pondered these issues in any detail. But when these heresies challenged the Church, Councils were convened and the doctrines concerning Christ were laid out explicitly, in great detail. Even though these beliefs were always held, they were not spelled out as clearly as they were when these heresies were dealt with. This same development has occurred with Mariology.
It is said by non-Catholics that Catholicism is a corruption of Christianity because it has added so much. However, two things must be stated. First of all, corruption can just as easily consist of deletions as it can additions. Secondly, nothing has been added in the Catholic Church, except for deeper insights into doctrines that have always been believed–greater developments, as it were. This was proved by Cardinal John Henry Newman. Starting with the corpus of Catholic doctrine in his day (1845), he traced back the Church's teachings and discovered that all of the Church's teachings could be traced back through successive centuries, right back to New Testament times. His findings were recorded in the book, Essay on the Development of Christian Doctrine. Newman, an Anglican when he wrote the book, soon thereafter converted to Catholicism. Protestants, on the other hand, do not attempt to trace their beliefs through the ages, because there was no Protestantism (or anything resembling Protestantism) for a period of 1400 years. They simply claim that the teachings found in the New Testament are similar to their beliefs. As Newman says, "To become deep in history is to cease to be a Protestant".
The development of doctrine goes back to the beginning. St. Vincent of Lirens sums up the ancient attitude when he writes: "Will there be no progress of religion in the Church of Christ? Certainly there is . . . But it is truly progress and not a change of faith. What is meant by progress is that something is brought to an advancement within itself; by change, something is transformed from one thing into another . . . The progress of religion . . . remain(s) what (it was) . . . Dogma may be . . . developed in the sequence of time . . . yet remain incorrupt and unimpaired . . . so that it does not allow of any change . . . The Church of Christ is a faithful . . . guardian of the dogmas which have been committed to her charge . . . In this sacred deposit, she changes nothing, she takes nothing . . . she adds nothing to it" (Commonitory 54, [A.D. 450]).