Well, actually, that passage's context is referring to the predestined.
But, you are definitely right that this is something we do not really know a lot about and God is a mystery on this issue to a great extent.
RW, I guess I am one of those dang free willers. I am also trying to use my brain here. If believers are predetermined, there would be no need to spread the Gospel of Jesus Christ. It would be predetermined. I believe the book of Matthew ends with Jesus telling us to go into all the world preaching the gospel. Why preach the gospel if believers are predetermined?