Note 3 at Eph. 3:3: The dictionary defines a "mystery" as "the quality or air of being unexplained, secret, or unknown" (American Heritage Dict.). The biblical mystery spoken of here is something that is secret or unknown until it is revealed, and can only be known by divine revelation (see ref. i on the word "mystery" in this verse). Paul stated in Galatians 1:12 that the gospel which he preached was not after man: "For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ."

According to verse 6, the mystery spoken of here not only involves the Gentiles sharing in the promise of the Messiah but also that Jews and Gentiles will be joint-heirs with the Messiah and incorporated into His one body. This is the mystery that was unknown in the Old Testament and revealed in the New Testament unto his apostles and prophets by the Spirit.