Yes, I know the story, though I wouldn't claim to know more than a few details. Even Jesus' disciples did not fully show cognizance of his Messianic role until after the resurrection. Spirituality is not conditioned on a full knowledge of events. It is a focus on and a knowledge of God, even if there is not a full awareness of what God is doing presently.
I wouldn't at all say that James was a pagan unbeliever in his upbringing, though that appears to be your inference? Not knowing his older brother's place as Messiah, or skepticism about it, is not the same thing as pagan unbelief! Mary clearly knew the prophecies about her son Jesus. And so, James had to be aware, as well. But James was subject to the same kind of skepticism and critical attitude that affects all of us.
I don't think James stepped into his Christian role out of paganism, or out of failure to believe in God. Under the Law James was probably fairly upright in his upbringing. Coming into a full knowledge of who is older brother was had to be an earth-shaking experience, even if he had long known of the prophecies surrounding him!
Reading James is an eye-opening experience, as he shows a full capture of Jesus' message in the light of Judaism. There is not a hint of jealousy or doubt at that point! I can't think of a more advanced or mature essence in a Christian letter. And James was not even one of the 12 chosen apostles!
Yes, I understand--thank you. I just don't agree that there is any real correlation, caused or not. Peter did not diminish. Israel did. Peter is still being read today, with great admiration. Israel is still viewed as a rejected people.