if indeed you have heard of the dispensation of the grace of God which was given to me for you, (3) how by that revelation He made known to me the mystery (as I have briefly written already…….(5) which in other ages was not made known to the sons of men, as it has now been revealed by the Spirit to His holy apostles and prophets: (6) that the Gentiles  should be fellow heirs, of the same body, and partakers of His promise in Christ through the gospel, (7) of which I became a minister according to the gift of the grace of God given to me by the effective working of His power.

The letter to the Ephesians was written by the apostle Paul while he was imprisoned in Rome for preaching the gospel. In our verses today Paul is expanding on earlier truths in this letter. He is confirming his divine authority for teaching the oneness of Jew and Gentile in Christ. In verse two I believe we can infer that knowledge of God calling the Gentiles wasn’t a problem and wasn’t addressed except in passing when Paul ministered at Ephesus.  It seems as if the controversy was raised later and Paul here is undertaking the defense of the gospel.  (He isn’t reminding the Ephesians of former statements.)

The doctrine of equal standing of Jews and  Gentiles in Gods eyes, in Christ, was a subject of many prophetic predictions. Even Jesus Christ spoke of it to his apostles. So my question is why is Paul saying this was not made known to the sons of men in other ages. I believe that there was no understanding – no information as to how the grace of God would be extended to the Gentiles.; that the manner of this accomplishment was unknown as the repeal of the ceremonial law was unknown. Paul was correct in calling this a mystery that was hidden – that was not understood. He is saying that by the Spirit and by divine authority, it is now revealed that Gods will and plan in Christ, was the admission of the Gentiles to be placed on a level with the Jews.
Remember that the gospel itself was a novelty. The world was truly turned upside down.