I guess I don't understand, from a strictly logical standpoint, why Socrates would be able to make it, but a comparable Chinese man living in the 1st century, or a Native American living in the 14th century, would be damned.
Plato/Socrates were known to preach contrary to the entire Greek way of life. They believed in natural virtue and (presumably) tried to live according to the natural law. As the saying goes, "grace builds on nature". God rewards those who live according to their conscience (as is everyone's duty).
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A study of history shows that the Chinese were not open to the Faith, even when missionaries finally went there after the middle ages. Even the great St Francis Xavier could barely make a few converts in Japan after years of toil. And Japan learned all their pagan ideas from China, so the two cultures were very similar. St Francis noted that once he learned about the Japanese culture, he said that the Chinese would have to be converted first, before Japan would follow.
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A study of native American history shows a similar thing. Most native tribes were utterly pagan and snake-worshipping. Their culture was based on war and death. Even the most anti-Catholic historians readily admit this. Much like the Aztec Indians who offered infants in sacrifice to their gods, the American Indians were ruthless. They didn't follow the natural law, so they would not be open to spiritual graces.
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The few exceptions of the American tribes show that when the missionaries arrived, they found that these Indians already knew about the one, true God and they recognized the "black robes" (as they called the priests) because God had sent them saints to preach the Faith. There is also ample historical evidence that the Russians, Celts and other countries traveled to America long before Columbus first arrived. They brought the Faith with them as well.