Exactly. That is what St Justin is saying, that Christ revealed Himself to Plato, just as Abraham was told about the Redeemer. Just as God miraculously sent St Peter to Cornelius in Scripture. Just as Blessed Mary of Agreda bilocated to preach to the American Indians. Just like St Thomas the Apostle was miraculously transported from India to see the Assumption of Our Lady with the rest of the Apostles. Just as St Padre Pio was transported to hear a dying man's confession who was on some remote snowy mountain.
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Our Faith tells us, and so does Scripture, that "God's hand is not shortened to save..." (Isaiah)
Are you saying that Christ revealed Himself to Plato *before his death?* If so, I mean... sure, he could have done that, but St. Justin doesn't say that, and at least seems to presume the possibility that he didn't.
I agree, of course, that anyone who is in Heaven has knowledge *now.* There are no Protestants in heaven. No Muslims. No Buddhists. No Hindus. No Eastern Orthodox. IF somehow any people who lived their lives as such were saved, despite their religions, they are certainly Catholic NOW.
The issue, as far as I understood it, was whether every soul had to believe in the Trinity and the Incarnation IN THIS LIFE in order to be saved, or if a soul who was invincibly ignorant of the Trinity and the Incarnation *COULD* be saved if they followed the natural law, etc. While I realize in the Old Covenant the level of knowledge required would've been different, it seems like the same principles Justin Martyr applies to Socrates, if accurate, COULD be applied to certain invincibly ignorant individuals after the coming of Christ *unless* there's something that I'm missing.
The more I get into this, the more I'm seeing that its a super complex issue because the exact terminology you use, at every point, matters.