Excellent article from Catholic New World.
In the fifth century, St. Vincent of Lèrins posed a question: “Is there to be no development of religion in the Church of Christ?” Today we could translate the question as: How can one preserve and transmit the precious deposit of the faith over time? In what sense can one speak of “the development of doctrine”?
Can there be a progress of religion in the Church of Christ?
Vincent of Lèrins answered as follows:
“Certainly there is to be development and on the largest scale. Who can be so grudging to men, so full of hate for God, as to try to prevent it? But it must truly be development of the faith, not alteration of the faith. Development means that each thing expands to be itself, while alteration means that a thing is changed from one thing into another. The understanding, knowledge and wisdom of one and all, of individuals as well as of the whole Church, ought then to make great and vigorous progress with the passing of the ages and the centuries, but only along its own line of development, that is, with the same doctrine, the same meaning and the same import.”
To explain his thought, St. Vincent of Lèrins uses an image unique to biology: The religion of souls should follow the law of development of bodies. Though bodies develop and unfold their component parts with the passing of the years, they always remain what they were. There is a great difference between the flower of childhood and the maturity of age, but those who become old are the very same people who were once young. Though the condition and appearance of one and the same individual may change, it is one and the same nature, one and the same person. Whatever develops at a later age was already present in seminal form; there is nothing new in old age that was not already latent in childhood. There is no doubt, then, that the legitimate and correct rule of development, the established and wonderful order of growth, is this: in older people the fullness of years always brings to completion those members and forms that the wisdom of the Creator fashioned beforehand in their earlier years.“In the same way,” Vincent of Lèrins concludes, “the doctrine of the Christian religion should properly follow these laws of development, that is, by becoming firmer over the years, more ample in the course of time, more exalted as it advances in age.” 
In Fr. Antonio Spadaro’s interview with Pope Francis for La Civiltà Cattolica, the Pope acknowledged that he often meditates on this passage and noted:
“St. Vincent of Lèrins makes a comparison between the biological development of man and the transmission from one era to another of the depositum fidei [deposit of faith], which grows and is strengthened with time. Here, human self-understanding changes with time and, so too is human consciousness deepened. In this regard we could think of the time when slavery was considered acceptable, or the death penalty was applied without question. So, too, this is how we grow in the understanding of the truth. Exegetes and theologians help the Church to mature in her own judgment. The other sciences and their development also help the Church in its growth in understanding. There are secondary ecclesiastical rules and precepts that at one time were effective, but now they have lost their value and meaning. The view that the Church’s teaching is a monolith to defend without nuance or different understandings is wrong.”
Beginning from the historic nature of the Church
Vatican II’s Dei Verbum (DV) highlighted the historic nature of the Church. It recognized that in the understanding of the tradition growth occurs when it is handed down according to the way in which the faithful contemplate the mysteries of the faith and treasure it in their hearts, advancing towards the fullness of divine truth:
“This Tradition which comes from the Apostles develops in the Church with the help of the Holy Spirit. For there is a growth in the understanding of the realities and the words which had been handed down. This happens through the contemplation and study made by the believers, who treasure these things in their heart (cfr Lk 2: 19, 51) through a penetrating understanding of the spiritual realities which they experience, and through the preaching of those who have received through episcopal succession the sure gift of truth. For as the centuries succeed one another, the Church constantly moves forward toward the fullness of divine truth until the words of God reach their complete fulfillment in her (DV 8).”
This conciliar statement illustrates the augmentative dynamism of the doctrine of the Church in the intellectual understanding of the Tradition, explaining how the historic process of the comprehension of the truth is the result of the action of the various individuals participating in the life of the Church, given that doctrine is built in an historic process of the creative intelligence of the people of God in tradition/transmission (paradosis). It is important here to note the importance given by the Council to the spiritual experience of the faithful. There is a clear indication that doctrine, in its dynamism, is intimately connected with the living history of the Church: in proclamation and in the keeping of the faith just as in spiritual deepening and in theological elaboration.
Vatican II’s Gaudium et spes (GS) has furthermore taught that “the Church guards the heritage of God’s word and draws from it moral and religious principles without always having at hand the solution to particular problems. As such she desires to add the light of revealed truth to mankind’s store of experience so that the path which humanity has taken in recent times will not be a dark one” (GS 33). Revelation is given in history, hence the doctrinal dynamism in the Church. The declaration Mysterium Ecclesiae of the Congregation of the Doctrine of the Faith, which dates to 1973, has emphasized the “historic condition that has an impact on the expression of Revelation,” wherever it is found, that is, in the Scripture, in the Creed, in dogma and then in the teaching of the magisterium. This means that a reformulation of how the faith is expressed, and in fact of the truth of the doctrine is appropriate, by clarifying it and giving it new expressive form, so that it may be effective in a pastoral context (cfr n. 5).
In this regard, John XXIII’s speech opening the Second Vatican Council remains foundational:
“What instead is necessary today is that the whole of Christian doctrine, with no part of it lost, be received in our times by all with a new fervor, in serenity and peace, in that traditional and precise conceptuality and expression which is especially displayed in the acts of the Councils of Trent and Vatican I. As all sincere promoters of Christian, Catholic, and apostolic faith strongly desire, what is needed is that this doctrine be more fully and more profoundly known and that minds be more fully imbued and formed by it. What is needed is that this certain and unchangeable doctrine, to which loyal submission is due, be investigated and presented in the way demanded by our times. For the deposit of faith, the truths contained in our venerable doctrine, are one thing; the fashion in which they are expressed, but with the same meaning and the same judgement, is another thing. This way of speaking will require a great deal of work and, it may be, much patience: types of presentation must be introduced which are more in accord with a teaching authority which is primarily pastoral in character.”
Therefore, when it comes to the deepening and the restatement of doctrine, we must take into account the vital link between the doctrine and the proclamation (kerygma) at the heart of the gospel. Pope Francis, in the apostolic exhortation Evangelii gaudium (EG), uses this principle both for the dogmas of the faith and for the moral doctrine of the Church:
“All revealed truths derive from the same divine source and are to be believed with the same faith, yet some of them are more important for giving direct expression to the heart of the Gospel. In this basic core, what shines forth is the beauty of the saving love of God made manifest in Jesus Christ who died and rose from the dead. In this sense, the Second Vatican Council explained, “in Catholic doctrine there exists an order or a ‘hierarchy’ of truths, since they vary in their relation to the foundation of the Christian faith.” This holds true as much for the dogmas of faith as for the whole corpus of the Church’s teaching, including her moral teaching (EG 36).”
There the Pope refers to an important principle affirmed by the Council: a “hierarchy of truths,” according to which expressions of faith or of doctrine vary in relationship to that which is fundamental (cfr Unitatis redintegratio, n. 11). This principle refers to the “rule of faith” or “rule of truth,” formulated in the second half of the second century in reference to pastoral practice, or rather to the concrete life of the Church, consisting of no fixed formulas on essentials for the Christian faith. This rule intended to set forth a fundamental hierarchy of the contents of the faith, expressing in fact the dynamism experienced by the Church.
In a speech delivered in Florence, on the occasion of the Fifth National Convention of the Italian Church, the Pope clearly traced his pastoral perspective regarding doctrine:
“Christian doctrine is not a closed system, incapable of raising questions, doubts, inquiries, but is living, is able to unsettle, is able to enliven. It has a face that is supple, a body that moves and develops, flesh that is tender: Christian doctrine is called Jesus Christ.”