How many people did the nation of Israel have, and how many were true believers?

Les teaches that the little nation of Israel never had more than probably 10 million people at the most, and only a few of them were true believers. He compares this to the wheat harvest: the main harvest fills the bins, while the corners are only a small fraction. Spiritually, Christ is the firstfruits, but the Church Age brings in the largest number. In the Old Testament economy, throughout Israel's history, very few Jews percentage-wise were believers. Even before the flood there were precious few believers, and by the flood only 8 souls. During Christ's earthly ministry, in Jerusalem and Judea, only 120 Jewish believers were gathered in the upper room in Acts chapter 1, though there may have been a few in Galilee. This is shocking after three years of the Lord's own earthly ministry, and it contrasts with the millions brought in through the Gospel of Grace.