First, Paul writes this part of the letter specifically to Gentile believers in the house churches of Ephesus (Eph. 3:1).
Second, Paul claims to be the recipient of something he labels “the stewardship of God’s grace,” given to him “for you,” for Gentile believers (Eph. 3:2, ESV). This stewardship, or this ministry of grace, is Paul’s way of describing the commission given to him to preach the gospel (“God’s grace”) to the Gentiles (compare Eph. 3:7, 8, ESV).
Third, Paul claims that a mystery has been revealed to him, a topic he has already written about in the letter (see especially Eph. 1:9, 10; Eph. 2:11-22), the “mystery of Christ” (Eph. 3:3, 4). Paul does not wish to be understood as the inventor of the gospel, but he does lay claim to a God-given ministry to proclaim it.
Fourth, Paul is not alone in having received advanced revelation about this mystery, as the Spirit has also revealed it to Christ’s “holy apostles and prophets” in a way that surpasses the revelation of God’s plan to earlier generations (Eph. 3:5). The term prophets here probably refers to those possessing and exercising the gift of prophecy among early Christian house churches rather than the prophets of the Old Testament. The mystery, which was once hidden, has now become what we might call an “open secret.”
Finally, he declares: “This mystery is that the Gentiles are fellow heirs, members of the same body, and partakers of the promise in Christ Jesus through the gospel” (Eph. 3:6, ESV).