Hi Ascanio. This can be a complicated theological dispute sometimes; but the real takeaway is this, (1) Pray, Work and Sacrifice for all to embrace the Catholic Faith, visibly enter the Church, and save their souls. (2) Love every person you meet and try to save them. And I would say, even, in trying to bring an erring person to the Faith, unless the contrary is evident (3) make allowance for possible good faith. That's my opinion. Others may disagree.
Btw, I'm not saying - neither did the Pope - that good faith is sufficient for salvation. In order to be saved, we must die as Catholics, believing in Our Lord Jesus, and being devoted to our Immaculate Mother Mary. Let there be no doubt, that we must give our children the very best Catholic Education that we can provide, teach them from an early age, to (1) Pray the Rosary every day, (2) Wear the Scapular and be Totally Consecrated to the Immaculate Mother of God, (3) Complete the Nine First Fridays, the Five First Saturdays, and the Great Double Novena of Nine Fridays and Saturdays, to the Twin Hearts together, (4) learn the Faith, and (5) become holy.
This is not about any of that at all. The question here, which can be very important for a Catholic Missionary evangelizing Protestants, for e.g. is whether or not separated Christians can sometimes be in good faith. That is an important pastoral matter to be aware of, because if we imagine every Protestant is a formal heretic (when the Church says, those who die as heretics are lost, She is speaking of formal heretics; recall that St. Augustine said those in good faith are not to be accounted heretics), then sometimes that very wrong assumption itself may prevent their returning to the Catholic Faith. I will give the example of a great Catholic Missionary Fr. Arnold Damen, who successfully reconciled 10,000 Protestants to the Catholic Church. Would you agree he did a great Apostolic Work, which all Catholics can admire, be proud of, and strive to imitate in their own measure, as they can, in desiring and working for the conversion of their own friends? I'm not saying we should not work for the conversion of Protestants, Heaven forbid! What I'm saying is they may sometimes be in good faith, and a good Missionary will in fact take that into account, in trying to return them to the Catholic Fold.
"in 1875 remarked that "a letter which arrived while I was there, announced to Father Rector the happy conclusion of a mission at Scranton, with 12,000 Communions, 19 converts, 200 adult First Communions, etc., but I found it was scarcely minded, such items being commonplace there. In 1879, after twenty-two years of excursions from Chicago, it was reckoned that Father Damen had conducted in person 208 missions, averaging two weeks time for each; he had travelled on an average of 6,000 miles each year; he and his different bands of companions together had given 2,800,000 Holy Communions and had made 12,000 conversions to the Faith. At one church in New York a party of his missionaries in the course of four weeks distributed no less than 42,000 Holy Communions." Thomas Hughes, S.J., Ms. notice of Father Damen. It may be interesting to note that General Longstreet was converted during a mission given by Father Damen in New Orleans in February, 1877, and that twenty-seven of Father's converts had been Protestant ministers"
https://www.olrl.org/apologetics/churchbible.shtmlNow, let's see how this Missionary Preaches: "Dearly Beloved Christians – When Our Divine Savior sent His Apostles and His Disciples throughout the whole universe to preach the Gospel to every creature, He laid down the conditions of salvation thus: "He that believeth and is Baptized," said the Son of the Living God, "shall be saved; but he that believeth not shall be condemned." (Mark 16:16). Here, then, Our Blessed Lord laid down the two conditions of salvation: Faith and Baptism. He that believeth and is baptized shall be saved, but he that believeth not shall be condemned – or is damned. Hence, then, two conditions of salvation: Faith and Baptism. I will speak this evening on the condition of Faith."
So Father begins by calling all of them Christians, not heretics - because not all of them would have been formal heretics. Some would be only in material heresy, what is called good faith. Who does Father say are not Christians at all? Only those who say, they refuse to believe something, that they know Jesus Christ to have taught. "I am sure there is not a Christian who will deny that we are bound to believe whatsoever God has revealed. Therefore, it is not a matter of indifference what religion a man professes. He must profess that true religion if he would be saved. But what is the true religion? To believe all that God has taught. I am sure that even my Protestant friends will admit this is right; for, if they do not, I would say they are no Christians at all."
This is exactly what St. Thomas taught. A formal heretic knowingly denies something Our Lord has taught. He doesn't care what Scripture teaches, he'll believe whatever he likes rather in the Lord's Teaching. But one in material heresy, or good faith, when the Catholic Faith is sufficiently proposed to him, from the Scripture for e.g. will begin to have doubts in his wrong understanding, and then, if he is of good will, would be gradually enlightened by God about the full Truth, till he arrives at the Catholic Faith. This is something the Church has taught, just as She by Her same authority has taught EENS for those stubbornly separated from Her. How can we uphold one if we deny the other? Both are true.
God Bless.