The Catholic Church as founded by Christ is essentially immutable in her constitution. This is the doctrine of the indefectibility of the Church, according to which it is impossible for the Church to depart from the path which Christ set out for her when He was on earth. It is impossible for the Church to fail in the carrying out of those functions which are most essential to her. This means that the Church could never change her doctrines or the meaning of them. The Church must always keep intact the deposit of faith. The Church could never teach or approve anything which would lead to the destruction of souls. The Church could never pass beyond the limits of the authority and power conferred upon her by Christ.
Divine tradition (often called “big-T” Tradition) is the sign of this essential immutability of the Church. Thus, tradition in this sense is itself immutable. The development of doctrinal understanding does not constitute any kind of real change in the doctrines contained in divine tradition. The dogmas themselves remain always the same, and it is impossible for them to change into something else. Hence it is impossible for the Church, in exercising her supreme authority, to teach anything contrary to these doctrines. What the Church teaches, she has always taught, in the same doctrine, the same sense, and the same understanding.
But there are other parts of the Church, not essential to the divine constitution, which are not so immutable. These are contained in what is called the ecclesiastical tradition (sometimes called “small-t” tradition). Though derived from the immutable doctrines of faith and morals just discussed, these traditions are extrinsic to them and subject to the prudential judgment of the Church. Hence they are, in theory, more able to be changed – or even abandoned if need be – without compromising the essential immutability and indefectibility of the Church.
However, there are strict prudential limits and rules which must be upheld in the changing of these traditions. The first of these rules is that the very purpose of these extrinsic, ecclesiastical traditions is to preserve and protect the outward identity of the intrinsic essence of the Church herself. The ecclesiastical traditions exist principally for the sake of protecting the divine tradition itself. As such, they grow and develop within the Church through the centuries in such a way that best suits the protection of the deposit of faith. According as these observances are well suited to the protection of the faith, they are maintained by the Church for whatever length of time she deems necessary. If they are found to be unsuitable in some way, they may be changed and improved upon, or even abolished. Otherwise they are presumed to be carrying out their function well enough to be maintained by all the faithful.
Generally speaking, then, an ecclesiastical tradition which enjoys the extent of a very long period of time is, for that reason, held to be better suited to protecting the deposit of faith. The longer a tradition has existed and contributed to the life of the Church, the greater certainty one may have that this tradition is the best that can be expected for the practice of the Faith – not that other options are necessarily unsuitable, but that they are less likely to be so, and experimentation would carry an unjustified risk. The rule of prudence dictates that, in general, an ecclesiastical custom should not be abolished if it has been established for a very long time. Thus, throughout the history of the Church there has always been an attitude of reverence and preservation towards tradition, while at the same time some traditions have died out when they no longer carried out their function. The rule of tradition is not incompatible with the necessities of changing times. But it was always considered an act of impiety to abolish a tradition which was healthy and flourishing and building up the faith of Catholics. Modifications were only introduced when a tradition was lacking in this respect.
Now, it is impossible for the Pope, in his official capacity as the supreme authority of the universal Church, ever to abolish or depart from a divine tradition of the Church. This is a consequence of the indefectibility of the Church (as explained above), as well as of the infallibility of the Church (according to the teaching of the First Vatican Council). But it is not impossible that the Pope may, in the exercise of his authority, depart from an ecclesiastical tradition of the Church. In so doing, he would not be violating the limits of his authority as such (for that is impossible), but the limits of the prudent exercise of that authority. For as just explained, whether the ecclesiastical traditions ought to be retained or changed is a matter which pertains to prudence. Hence Pope Leo XIII writes that "it is not the part of prudence to neglect that which antiquity in its long experience has approved..."
It is important to stress that despite exercising his authority imprudently, nonetheless the Pope cannot approve or teach anything which is contrary to the deposit of faith. This means that even in the act of imprudently changing or abolishing an ecclesiastical tradition, the Pope could not depart from anything that is contained in the divine tradition. Thus, although a papal act abolishing an ecclesiastical tradition may be imprudent or even immoral (by reason of extreme imprudence), nonetheless, that which the Pope approves by such an act cannot itself be immoral or evil in any way. This is a critical distinction: the act of change must be considered apart from the substance of what is being changed. Therefore it is possible that, while the state of being without an immemorial ecclesiastical custom is not evil or harmful in itself, it may nonetheless have been brought about by an act of imprudence if it clears the way, as it were, for some possible future harm.
Thus, for example, although the Church would not illegitimately or fallibly promulgate a law whereby communion under both species was reinforced, nonetheless this would be gravely imprudent, since it might appear to indicate a doctrinal error, namely that the entire Christ is not equally present under each species. But in promulgating such a law, the Church would not actually be contradicting the true doctrine of the faith, and thus the discipline could not be intrinsically harmful or evil (this is also evident by the fact that the Church did at one time allow this practice). But to promulgate such a law would indeed be gravely imprudent, even immoral, since it would be accompanied by the possibility of causing serious confusion in the minds of the faithful.
Or to use another example, although the Church would not err in faith or exceed her authority were she to impose a law whereby the elevation at mass was to be discarded. Nonetheless, this would be gravely imprudent and immoral, since by so rashly abandoning one of her own traditions, she would appear to be denying the very reason for which that tradition came into being in the first place, namely, the reverence and veneration due to the Real Presence. But such a law would not in itself be contrary to faith; after all, the elevation has not always been practiced in the Mass. In the promulgation of such a law, it would not and could not be the case that the Church had in fact denied the true doctrine, only that she might appear to have done so. Obviously, there would be a harm here caused not by a departure from true doctrine, but by a lapse in prudential judgment on the part of the Church.
This is all a consequence of the fact that ecclesiastical traditions exist precisely as a means of expressing true doctrine in the minds of the faithful. It has always been acknowledged by Catholics that to abandon such a tradition, especially one which has long been in force, is the height of rashness and impiety, because in doing so one opens the door, so to speak, for harm to come to the faith. Ecclesiastical tradition is like a great fortress surrounding a treasure of inestimable worth, namely the faith. To tear down that fortress is not necessarily to harm the treasure; but it would be the height of imprudence, since doing so would leave the treasure susceptible to possible harm. Now, one might propose replacing the fortress with another; but why do this when the already existing fortress has served its purpose to perfection for a great length of time? To replace it hardly seems necessary, and there is the risk that the new fortress will be less perfect in its function. It is essentially the same with tradition – indeed, more so.
The implications with regard to the modern liturgy should be evident. On the one hand, one ought to conclude on this evidence that there is a definite problem with the New Mass insofar as, in practice at least, it results from an abandonment of immemorial ecclesiastical tradition. This itself is evident from the fact that the New Mass is just that: a new mass. Authoritative voices in the creation of the Novus Ordo have testified to its novelty, such as Archbishop Bugnini (the main author of the new text), Fr. Joseph Gelineau (one of Bugnini's collaborators), and Pope Paul VI himself. But an actual examination of the text of the new liturgy reveals a very stark departure from the traditional prayers in both content and meaning. The liturgical formulas and expressions traditionally used by the Church have been replaced by language that is imprecise, susceptible to doctrinal misinterpretation, and devoid of spiritual depth.
On the other hand, none of these prayers say anything which is actually false or contrary to the faith, and therefore nothing which is directly harmful to the faith. Pope Paul VI had every legal right to establish the Novus Ordo as an official rite of the Church, and he did not depart from his divinely granted authority in doing so. The fact that the prayers contain nothing actually false in them is evidence that Paul VI was truly protected by the Holy Ghost in sanctioning those prayers. The harm lies not in anything intrinsic to the reformed liturgy, but in the imprudence of abandoning a liturgy that was doctrinally unambiguous, theologically deep, and spiritually rich, and replacing it with relatively shallow and weak expressions of the Catholic faith. It is evident that the change itself - as distinct from the content of the new liturgy considered on its own merits - by virtue of being such a radical departure from immemorial ecclesiastical tradition, was a serious error on the level of prudence.