“So long as the member was on the body, it lived; separated, it lost its life. Thus the man, so long as he lives on the body of the [Catholic] Church, he is a Christian; separated from her, he becomes a heretic” (Encyclical Satis cognitum of June 29, 1896).
Please, Don’t Call Protestants Christians by Marian T Horvat

And yet, this SAME POPE considered the sacraments offered by the "heretical" Eastern Orthodox as being "valid." Why would sacraments offered by a "heretical" Church STILL be considered "valid"? Does that sound like sound doctrine to you? 

 Shouldn't ANY and ALL sacraments offered by a heretical and or schismatic Church be completely illicit AND invalid because they are being conferred and offered by heretics who have separated themselves from Christ???

If you will read St. Thomas Aquinas, you will understand how the Sacraments can be "valid" but confer no grace on the recipient if the recipient is heretical. This applies to the Orthodox. The Protestants are much worse off.

Unfortunately, St. Thomas erred on several significant issues of faith. He denied, for example, the Immaculate Conception and to do so on such a significant rule of faith makes the rest of his statements, even those on sacramental theology, "questionable" at the very least. After all, he blended Aristotle's pagan philosophy with Christian teachings despite the fact that both St. Paul and St. Antony of the Desert explicitly warned Christians against adopting "philosophy" to their "theology." 

Where did I state you were a heretic?

I apologize. I confused you with the member WorldsAway who said that.

Any soul that is validly baptized receives an indelible mark on his soul and becomes a child of God. The Holy Spirit takes up His abode in that soul.
Prior to Vatican ll, the Church never referred to Protestants or heretics as Christian.  Unfortunately even Traditional Catholics have adopted the false modernist language of calling Bible readers, Christian.

So, the character of Baptism doesn't alone suffice to make someone a "child of God".  That requires also having the necessary dispositions to enter into a state of justification.  So, an adult Protestant who gets baptized does not thereby become a child of God.

Everyone should just ignore this heretic, who goes around deposing Popes based upon his own extraordinary intellect ...

Of course, he never bothered to look at the Latin of the time Leo XIII used what has been translated as "separated brethren" (I'm sure rather deliberately by the Modernists, possibly even the Americanists he had been at odds with).

But this intellectual giant here, who may possibly be able to decline a simple first declension noun, if he were looking for truth, would see that the Latin is ...

fratres dissidentes

... which better translates to dissidents, as it's an active departure, using a verbal (gerund) form with an active voice, where the activity was the result of their volition ... and not a term like "separated", which is more passive and could be something entirely unintentional -- so like the difference between a child who got separated from his parents (say, in a crowd) vs. a child who rebelled form his parents and broke away from them (which is more the term "dissidentes", very similar to the English word we have that derives from it).

As for the term "brothers", as already been explained, we can be "brothers" in a natural sense, since we have the same Father, the same Creator, and this does not mean that they are fellow "Christians" in the theological sense (vs. the natural sense in which these groups might be called Christians ... as opposed to something else, like Muslims or Jews), or somehow still members of the Church, as this heretic here would slander the Pope as teaching.

In fact, Pope Leo quite emphatically teaches the EXACT OPPOSITE, spending nearly the entirety of Satis Cognitum on the subject:

Satis Cognitum:

Quote "There is one God, and one Christ; and His Church is one and the faith is one; and one the people, joined together in the solid unity of the body in the bond of concord. This unity cannot be broken, nor the one body divided by the separation of its constituent parts" (S. Cyprianus, De Cath. Eccl. Unitate, n. 23).
...
"Whosoever is separated from the Church is united to an adulteress. He has cut himself off from the promises of the Church, and he who leaves the Church of Christ cannot arrive at the rewards of Christ....He who observes not this unity observes not the law of God, holds not the faith of the Father and the Son, clings not to life and salvation" (S. Cyprianus, De Cath. Eccl. Unitate, n. 6).
...
The practice of the Church has always been the same, as is shown by the unanimous teaching of the Fathers, who were wont to hold as outside Catholic communion, and alien to the Church, whoever would recede in the least degree from any point of doctrine proposed by her authoritative Magisterium. Epiphanius, Augustine, Theodoret, drew up a long list of the heresies of their times. St. Augustine notes that other heresies may spring up, to a single one of which, should any one give his assent, he is by the very fact cut off from Catholic unity. "No one who merely disbelieves in all (these heresies) can for that reason regard himself as a Catholic or call himself one. For there may be or may arise some other heresies, which are not set out in this work of ours, and, if any one holds to one single one of these he is not a Catholic" (S. Augustinus, De Haeresibus, n. 88).
...
But he who dissents even in one point from divinely revealed truth absolutely rejects all faith, since he thereby refuses to honour God as the supreme truth and the formal motive of faith.

Contrary to the Vatican II teaching of a "Church of Christ" which is not co-extensive with the Catholic Church, Leo XIII teaches Traditional Catholic doctrine.

Now, one MIGHT use the term "brothers" or the term "Christian" in the natural sense, brothers being children of the same Father and Creater, according to nature, and "Christian" as referring to a natural classification rather than a theological one, but the actual ecclesiology of Pope Leo XIII that transcends semantics, especially as interpreted by someone who either is not able to or else is too lazy to actually look at the Latin, and then properly understand the meanings of terms.


At no point does Leo XIII state that heretics are somehow within the same Church as Catholics nor that they belong to the same body.

And your "separated brethren" quote should be read in the context of John 15. They are "separated" from the living Vine, the one true Church, the Body of Christ. They get no grace, life, from the Sacraments. Unless they reunite with the Vine, they will wither and be burned in the fire.

As I pointed out, the term is not even "separated", except in the (deliberately?) faulty translation.

It's DISSIDENT brethren ...

Unfortunately, St. Thomas erred on several significant issues of faith. He denied, for example, the Immaculate Conception and to do so on such a significant rule of faith makes the rest of his statements, even those on sacramental theology, "questionable" at the very least. After all, he blended Aristotle's pagan philosophy with Christian teachings despite the fact that both St. Paul and St. Antony of the Desert explicitly warned Christians against adopting "philosophy" to their "theology."

And, again, nobody calls this jackass out for rejecting scholasticism in principle, something which several Popes have endorsed and promoted.  That application of "pagan philosophy" to "Christian teachings" (aka Revelation) is precisely the very textbook definition of scholasticism.  So this joker deliberately conflates the fact that St. Thomas makes some mistakes on specific topics with a repudiation of scholasticism in principle.

Of course, we see the fruits of this moron's rejection of applying "philosophy" (and logic in particular) to doctrine, i.e. actually engaging in what the scholastics referred to as theology ... by his floudering from one heresy to he next, bumbling and fumbling around aimlessly.

There can be general warnings about philosophy in that there were many aberrant scholols out there, and in fact some of the Fathers were a bit excessively Platonic, albeit with revision and modification, and therefore neo-Platonic, but Aristotle's contribution to just the general state of human knowledge and reasoning was absolutely monumental.

While God left a certain Deposist of Revelation, the minute that human beings start to think about, to interpret, and to apply the principles that have been revelead, to other situations and cases ... that's when you must have a systematic way of simply differentiating between solid reasoning and erroneous reasoning ... and we see the latter here in spades with this poster here.

Graces builds upon and perfects nature, but does not destroy it.  So it's very useful to have an understanding of the nature that God created, as well as about how our minds work toward the acquisition of truth (and error).