Even if you don’t think the New Testament letters prove that Jesus Christ and was the Son of God, you have to admit that they do show that a lot of people certainly thought that. Similarly, the theology in the New Testament epistles could one supposes be challenged or rejected if their Scriptural authority is not accepted. But it would remain true that the letters would not have been written at all if the authors had not believed in the existence of Jesus Christ and, given the context, His divinity and Resurrection. And if they themselves had known Jesus — and even if others at one step removed knew those who had directly known Jesus — then that tells us something about the likelihood of Jesus’ divinity, does it not? Historical proximity is important here. Peter’s letter cannot be likened to David Koresh’s.
And then there’s the problem of a counter-narrative: How would a nonbeliever explain why the letters were written? It is not possible to deny credibly that the writers really believed the truth of what they were writing. What motive would they have, what reason for some sort of vast, trans-Mediterranean conspiracy to spread a big and blasphemous lie knowingly? Peter and Paul and the rest did not become wealthy men of leisure; they could have gotten by more easily and safely by fishing or making tents. So the counter-narrative must be that a lot of people who knew Jesus came to believe, live, and die for a preposterous notion of who He was. And how credible is that?
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But one might also ask: Why did so many people back then not accept Christianity?
As a psychological matter, there are two obvious reasons. First, no doubt about it, its supernatural claims seem incredible. Second, accepting them would require a complete rethinking of big chunks of one’s life: certainly religion, but also secular aspects of one’s existence — and there might be heavy social and legal penalties for rejecting the status quo. There would be a powerful inclination to ignore or dismiss the whole business.
Think of something similar happening today, or indeed similar things that are in fact happening. People do not readily abandon comfortable lives and long-held beliefs. And it’s not just atheists clinging to their rejection of God despite mounting evidence to the contrary: If it were somehow definitively shown that Muhammed or Jesus never existed, would you expect and wholesale and immediate end to Islam and Christianity? No, there would be efforts to undermine or ignore the evidence.
Those are the psychological reasons why Christianity might have been rejected by many in the first century, but there are practical reasons, too, that obtained then more than now. Communication was slower and more difficult. There were no photographs or newspapers of record, to say nothing of televisions and iPhones. Literacy rates were much lower anyway, and people were less educated. So when — and if — claims drifted in from abroad, you could believe your “tribe” or someone else’s: an easy choice.
And, pace Paul, to an extent becoming a Christian early on was becoming a Jew albeit a new sort of Jew — and what non-Jew at the time wanted that?
My point here is of course not that nonbelievers were right in not believing, but just that their nonbelief is no evidence that the New Testament epistles were false.
Oh, and one last thing: Despite these understandable reasons not to believe, it is remarkable that very soon an astonishing number of pagan gentiles did become Christians. What are we to make of that?