I recently invited a number of prominent Catholic apologist and theologians (specifically Karl Keating, Jimmy Akin, Michael Voris, and Marcellino D’Ambrosio, but open to anyone who has an apostolate ordered toward defending the Faith) to answer what I believe to be one of the most important questions of our time:

Is Mortalium Animos still the faith of the Holy Catholic Church?

Jimmy Akin / November 1, 2014:

Mortalium Animos is a papal encyclical and thus a papal document.

Documents are not the objects of faith. God and, by extension, those things that he has revealed and those things that the Church has infallibly defined are.

If something has been revealed by God then it is an object of divine faith. If something has been infallibly defined by the Church then it is an object of ecclesiastical faith. If something has been both revealed by God and infallibly defined by the Church then it is known as a dogma.

Mortalium Animos mentions a number of dogmas in passing (e.g., the Trinity, papal infallibility), but it is not itself one big definition of dogma. In fact, the document does not contain any new definitions at all. The propositions contained in Mortalium Animos have varying levels of doctrinal authority that have to be assessed in terms of both prior and subsequent magisterial teaching.

Like other magisterial documents, it may also contain propositions that properly speaking are not doctrinal but prudential or that are contingent and involve the application of doctrinal principles to particular situations.

Also, any propositions that are not infallible definitions are also potentially subject to doctrinal development. How particular propositions are to be interpreted and applied to the present situation must be assessed according to the hermeneutic of renewal in continuity articulated by Pope Benedict XVI.

Louie Verrecchio / November 1, 2014

So, if I understand you correctly, certain parts of MA are in fact applicable to the present, while others may not be…

How about this: I’ll provide what I consider the most crucial relevant parts of the document; i.e., those that appear to condemn the modern ecumenical movement most directly, and you can let me know if I am misreading it. Does that work?

Jimmy Akin / November 1, 2014:

Yes, you’ve understood me correctly… The course you suggest is good way to proceed.

Louie Verrecchio / November 3, 2014:

The stated purpose of this exercise is to evaluate the degree to which MA reflects the faith of the Church relative to the work of ecumenism such as it is carried out in our day; a work ordered on the “quest for unity.” (cf Ut Unum Sint)
First, it’s necessary to have a working definition of “unity” and how it is realized among Christians as understood and taught by the sacred Magisterium throughout the centuries.
Even though we’re focusing on Mortalium Animos in particular, it must be noted that in speaking of “unity” therein, Pius XI is simply passing on what he received; e.g., the matter of unity as treated in Satis Cognitum of Leo XIII in which Sacred Scripture and the Fathers of the Church are drawn upon extensively. (As you said, there are no new definitions to be found in MA.)
With that said, Pope Pius XI states, “the disciples of Christ must be united principally by the bond of one faith.” (MA 9)
Further on, he states, “How so great a variety of opinions [such as the false opinions of the heretics re: the Eucharist, the papacy, Blessed Mother, etc.] can make the way clear to effect the unity of the Church We know not; that unity can only arise from one teaching authority, one law of belief and one faith of Christians.” (ibid.)
The Holy Father then gets to the central point, saying, “the union of Christians can only be promoted by promoting the return to the one true Church of Christ of those who are separated from it.” (MA 10)
Pius XI then goes on to define in very concise terms the fundamental requirement for being in, and remaining in, this one true Church of Christ, saying,  “Furthermore, in this one Church of Christ no man can be or remain who does not accept, recognize and obey the authority and supremacy of Peter and his legitimate successors.” (MA 11)
One notes the unambiguous wording; “the disciples of Christ must be… that unity can only arise… the union of Christians can only be… in this one Church of Christ no man…”
My understanding is that the above quoted teachings are most certainly the faith of the Church today; indeed, these teachings are immutable as they reflect the constant witness of sacred Tradition (they are part of the universal ordinary Magisterium) and are founded upon Sacred Scripture.
As such, we must believe that apart from that union among those Christians who are in, and remain in, the one true Church of Christ as defined in Mortalium Animos (as referenced above), there can be no “unity” properly understood.
Do we agree on at least this most basic proposition?

Jimmy Akin / November 4, 2014:

I have a concern that the question of whether something is “the faith of the Church” may unnecessarily complicate our discussion.
As mentioned in my first reply, a matter of faith may either be an object of divine faith (meaning it is revealed by God) or an object of ecclesiastical faith (meaning it has been infallibly proposed by the Church).
If the guiding principle of the discussion is the question of whether something is an object of faith then that will cause us to have to stop and consider, for every proposition under discussion, whether it is divinely revealed or whether it has been infallibly proposed by the Magisterium.
This could have the effect of bogging down the discussion.
I propose that, instead, we ask the question “Is this Church teaching?”
It is, in general, an easier matter to determine whether something is Church teaching than if it is a matter of divine or ecclesiastical faith, and this would allow us to agree on more propositions more swiftly and so speed the discussion.
It may become necessary, at various points, to stop and look into the question of whether a particular point is a matter of divine or ecclesiastical faith.
I’m happy to do that when needed, but I’d rather not have to do it for every single point if we are otherwise agreed that something is a matter of Church teaching.
Please let me know if this is acceptable.
On the assumption that it is, here are some thoughts on the passages you quote from MA.
First, I take the unity that Pius XI considers the goal to be the full, visible communion referred to by John Paul II in Ut Unum Sint 77. As the latter pontiff indicated in that passage, full communion presupposes “full unity in faith.”
I thus think that John Paul II is articulating, in different words, the same basic principle that Pius XI articulated when he said that “the disciples of Christ must be united principally by the bond of one faith” (MA 9).
I thus take this to be Church teaching, both in Pius XI’s time and in our own.
For there to be “full visible communion,” there must be “full unity in faith,” which entails the acceptance of the various dogmas mentioned in MA 9. In particular, it includes a recognition of the role of the pope, including his ability to define dogmas ex cathedra, as stressed in UUS 94 (cf. MA 11).
I would concur with the statement that “‘unity’ properly understood”–i.e., the full visible communion referred to in UUS–is achieved only when a person is fully incorporated into the Catholic Church.
This represents the teaching of the Church both in Pius XI’s day and in ours.

Louie Verrecchio / November 5, 2014:

I’m afraid we’re going to be stuck on GO for a moment longer…
It would seem that the very concept of an “ecclesiastical faith” understood as distinguishable from “divine faith,” even if widely accepted among theologians today, is debatable. (Good article by Msgr. Joseph Fenton http://strobertbellarmine.net/fenton_ecclesiastical_faith.html )
This is another topic altogether, however, and not applicable to the present discussion.
That said, perhaps “faith of the Church” is not the best phraseology either.
In any event, the treatment of Christian unity that I excerpted from MA is a matter of divine faith since it is founded on Sacred Scripture and has been constantly held in the Tradition of the Church, and is therefore understood to be infallibly taught via the universal ordinary Magisterium.
I’m not suggesting that you disagree with this, but just to be sure, it would seem that agreement on this note is important in order to proceed fruitfully.
I also feel compelled to address the introduction of Ut Unum Sint as a point of reference.
Ultimately we may want to consider if, and to what degree, UUS is a departure from MA (and I suppose it is no secret that I see this document as a considerable departure) but for now I think it’s important to focus on MA, and to the extent necessary, that which preceded it, exclusively in order to avoid confusion. We’ll see how the present day ecumenical movement measures with MA afterwards.
To illustrate: You said, “I take the unity that Pius XI considers the goal to be the full, visible communion referred to by John Paul II in Ut Unum Sint 77.”
Properly speaking, however, Pius XI, beyond expressing a desire for heretics to return to their Holy Mother, does not speak of unity in terms of being a “goal,” whereas JPII does; i.e., their respective treatments are so different, and in certain places truly incompatible, that reference to the latter is a can of worms best left unopened at present, even though I do look forward to opening it eventually.