Was the mystery of the Church Age known before Paul?

Les explains that the Body of Christ, what we now know as the Church Age, is strictly a Pauline revelation. It is not associated with the promises given to Israel, but is that unique outpouring of the grace of God upon the Gentile masses, so that they can experience salvation and become children of God by faith plus faith alone in the Gospel, thereby becoming members of the Body of Christ. Israel, in the meantime, has spent the last 1900 and some years in spiritual blindness, according to the Old Testament as well as Paul. Les points out that since the Body of Christ is strictly a Pauline revelation, you will not find it anywhere else except in the letters of Paul. Paul is the one in 1 Corinthians chapter 15, verse 51, who says, “Behold, I show you a mystery, which up until his time had been kept secret in the mind of God.” Les says these things were kept secret in the mind of God until He saw fit to reveal it to this Apostle. Paul then says, “I show you a mystery, we shall not all sleep, we shall not all die, but we shall all be changed.”