Paul first introduces the concept of “the mystery” in Ephesians 1:9. He returns to this imagery three times in chapter 3. However, in each text, Paul clarifies that the mystery of God’s will and the “mystery of Christ” (3:4) has been revealed. Additionally, it has not been made known to a select few, but rather to all men. Consider the following:
Ephesians 1:9 – “having made known to us the mystery of His will”
Ephesians 3:3-4 – “how that by revelation He made known to me the mystery (as I have briefly written already, by which, when you read, you may understand my knowledge in the mystery of Christ”
Ephesians 3:8-9 – “that I should preach among the Gentiles the unsearchable riches of Christ, and to make all men see what is the fellowship of the mystery”
So then the question is, what is the identification of this now revealed “mystery?” The language here used by Paul is also used by him elsewhere and sheds some light on what Paul is talking about.
With regard to Ephesians 3:3 and the revelation of the mystery to Paul, consider Galatians 1:11-12, wherein Paul, speaking of the gospel he preached, declared, “For I neither received it from man, nor was I taught it, but it came by revelation of Jesus Christ. So, Paul here speaks of the gospel being revealed to him.
Consider also Paul’s statement in Ephesians 3:8 concerning what he preached among the Gentiles. Again, we turn to Galatians for clarification. In Galatians 2:7, Paul writes “that the gospel of the uncircumcision had been committed to me.”
So, we have the mystery given to Paul by revelation and the gospel given to Paul by revelation. Then we have Paul preaching the mystery among the Gentile, and we also have the gospel committed to him on behalf of the Gentiles.
Finally, note how Paul says in Ephesians 3:5 how the mystery was formerly hidden from men, but “has now been revealed by the Spirit to His holy apostles and prophets.” So what message was hidden with God until He chose to reveal it by the Spirit through the apostles and prophets? The gospel of Jesus Christ, which was first preached by the apostles through the inspiration of the Holy Spirit in Acts 2. Thus, the mystery is the gospel, God’s plan to save man (Rom 1:16).