Did the Jews understand the mystery that Paul revealed?
No, the Jews did not understand the mystery. The context states they had no concept and would have reacted with horror to such a subject. The mystery was hid in God from the beginning of the age and revealed through Paul, making all men see the fellowship of the mystery.
Les explains that the Jews had no concept of the mystery. They would have thrown up their hands in horror if anyone approached such a subject. The mystery was hidden in God from the beginning of the world or age. God sovereignly kept it secret. Paul was made a minister to reveal it, so that all men, not just Israel or Gentiles, might see the fellowship of the mystery. Another aspect is that Israel would be spiritually blinded for almost two thousand years, while Gentiles come into a privileged position in the body of Christ.