What did much of the Jewish community refuse to believe about Jewish believers in Christ?
Much of the Jewish community refuses to believe and will not admit that any Jews ever became followers of Christ. They reject the idea that Jewish people became believers in Him. It is a blanket denial that Jewish people ever followed Him.
Les explains that much of the Jewish community refuses to believe that, and they won't admit that any Jews ever became followers of Christ. In this context, Peter is speaking to the nation of Israel, appealing to the God of Abraham, Isaac, and Jacob, the God of their fathers. He accuses Israel of delivering up and denying Jesus in the presence of Pilate, even though Pilate was determined to let Him go, but Israel insisted. Thus, the refusal is specifically a denial that Jewish believers in Christ ever existed.