Mysterious Mystery

Why is the Ephesians 3 “mystery” a mystery to modern saints?

Paraphrase of Reverend Sadler from Chapter 9 of The Second Adam and The New Birth:

“In Ephesians 3, Paul asserts his claim to be the instrument of God for spreading far and wide the knowledge of a mystery hid from ages and generations. He calls himself “the prisoner of Jesus Christ for you Gentiles.” He endured imprisonment, that is, not merely for preaching Christ, but for preaching the acceptance of the Gentiles on equal terms with the Jews in the Church of Christ.

What does the Apostle Paul dignify with the name of “mystery of Christ”? Is it the Incarnation or the Atonement? Is it the Predestination of certain individuals in the invisible church without regard for the visible church? Paul tells us that the mystery is “that the Gentiles should be fellow heirs, and of the same body, and partakers of God’s promise in Christ by the Gospel.”

In our day, because we have enjoyed so many blessings of the Gospel for so many hundred years, we find it very difficult to realize why Paul would be considered so special for being the instrument for that particular understanding of the “mystery.”

To Paul and his countrymen, this mystery was of such a nature that it hindered the ancient people of God from receiving the Gospel, but we cannot even fathom it as a mystery at all. We have had the kingdom of God transmitted to us through the ages as a matter of course – a thing to which we imagine we have rightful title.

The reception of the Gentiles into the Church of Christ is to us so plain and familiar a matter, that it is difficult to understand how it could ever have been a mystery in any sense.”

Sadler goes on to explain how this difficulty in appreciating the context of Paul's letter and the word "mystery" has led to anti-church sentiments under the guise of the "invisible / visible" distinction, through which some have attributed a position to Paul which he actually opposed.