As for the Parable of the Sower. Jesus says, “he who has ears to hear, let him hear.” In that quote, does it not leave the possibility of those who do not have ears to hear? In tha parable, (Luke 7:4-8), there is no mention of those plots of land without seeds. Maybe they are destined to be barren, or maybe it is something else. But because of this, when looking at this parable, we cannot know what happens to non-Catholics who have never given seeds. There are other places that talk about the faith, but I’m just referring to this one to stay on topic of your post.
If you don’t have fruit, you cannot be saved. That is a fact. If you never have a seed, you can’t have a plant and if you don’t have a plant you can’t have fruit. To state the argument that you are missing, you would need to argue that if one was not Catholic he could still receive seeds from the limited truth available to him and somehow manifest perfect contrition and charity and thereby have a plant capable of producing fruit.
Here’s what is meant by having “ears to hear” as explained in Haydock’s Commentary drawn from the fathers:
Mat 13:9
He that hath ears to hear. By these words, we are exhorted to examine the meaning of the parables. (St. Jerome) See Chap. xi. 15. — We are also taught that not all, but only such as have had the sense of the Scriptures opened to their understanding from above, can properly understand them. The apostles themselves were in ignorance till Jesus Christ gave them the true meaning: aperuit illis sensum, ut intelligerent Scripturas: “he opened their understanding, that they might understand the Scriptures.” (St. Luke xxiv. 45.) It is God who speaketh in the Scripture, and it is God who giveth us to understand what is therein delivered.
His truths he conceals from the proud, while he reveals them to the little and humble. How can any persons pretend that the most mysterious, as well as the most sacred book in the world, is open to every understanding? St. Paul (Acts xiii. 26.) tells the Jews, that although the Scriptures were read to them every sabbath-day, their very rulers did not understand them; and St. Peter, in his 2d Epistle (iii. 17.) assures us, that there are many passages hard to be understood. — all comes from God.
It is He who openeth our ears to hear, our heart to believe, and our mind to understand. Agar was near a well, and yet she wept, because she had no water to give her son to drink, God opened her eyes, and she saw the well that was close to her. Thus, says Origen, we may read the Scripture, and find no nourishment for the soul, unless God opens our mind, to see therein on what we are to nourish it. It contains salutary waters, but only those can be benefited by them, who see how to drink of the heavenly source. It is the Holy Ghost alone who can effectually open our eyes, to see these waters that spring up to life eternal; and this special grace we are to obtain by humble and fervent prayer. Knock, and it shall be opened to you.
And if you read the full context, Christ actually does speak about those who do not have “ears to hear.”
He that hath ears to hear, let him hear. And his disciples came and said to him: Why speakest thou to them in parables? Who answered and said to them: Because to you it is given to know the mysteries of the kingdom of heaven: but to them it is not given. For he that hath, to him shall be given, and he shall abound: but he that hath not, from him shall be taken away that also which he hath. Therefore do I speak to them in parables: because seeing they see not, and hearing they hear not, neither do they understand. And the prophecy of Isaias is fulfilled in them, who saith: By hearing you shall hear, and shall not understand: and seeing you shall see, and shall not perceive. For the heart of this people is grown gross, and with their ears they have been dull of hearing, and their eyes they have shut: lest at any time they should see with their eyes, and hear with their ears, and understand with their heart, and be converted, and I should heal them. But blessed are your eyes, because they see, and your ears, because they hear. For, amen, I say to you, many prophets and just men have desired to see the things that you see, and have not seen them: and to hear the things that you hear and have not heard them. (Matthew 13:9-17)
The Pharisees did not have their understandings opened and therefore did not have “ears to hear.”
Interesting side note in reference to this parable:
And as we find that only one-fourth part of the seed produced fruit, we may thence infer how many and great are the obstacles in the way of salvation, and how few will be the number of the elect. (Haydock)
So those without the proper baptism into the Catholic faith can bear good fruit because the law of God is written in them. This does not mean that people can simply choose not to join the Catholic Church if they know that this is the Church Christ built and is continuing to shape. However, it not quite what you are saying Una Fides.
If one is not been baptized in the Church, he cannot bear fruit, for if one has no seed, he has no roots or tree, and if he has no tree, he cannot possibly bear fruit. Otherwise, where would the fruit be coming from? You need to be a branch attached to the Vine in order to produce fruit. To be a branch attached to the Vine, we must “abide” in him. This word “abide” is also used in reference to receiving Christ in holy Communion (John 6), so to abide we must be receiving Christ in his sacraments so we can produce fruit.