Can you help me explain Eph. 2:19-20 . If I tell people that Paul’s gospel differs from kingdom gospel some say these verses refer to Peter in Matt. 16. When Paul mentions Apostles, is he referring to the 12?

When Paul wrote of the Body of Christ and said: “Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God; And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;” he was not saying we are built on what Peter and the 12 taught. Notice the order “apostles and prophets.” When God formed the Body of Christ according to I Corinthans 12:28 “God hath set some in the church, first apostles, secondarily prophets” Paul was the first and foremost apostle but even in Ephesians 4:8 and 4:11 “When he ascended up on high, he led captivity captive, and gave gifts unto men….And he gave some, apostles; and some, prophets; and some, evangelists; and some, pastors and teachers.” Notice the order and that he did this after he ascended into heaven. But when God was dealing with Israel he first gave them prophets (the Old Testament) and in Jesus Christ’s earthly ministry he gave them apostles. That is why the order differs in Luke 11:49 where it says “Therefore also said the wisdom of God, I will send them prophets and apostles, and some of them they shall slay and persecute.” We are not built on them but on the apostles and prophets Jesus Christ gave after he ascended to heaven starting with Paul and the information found in his epistles.

Now concerning the gospel Paul preached. According to I Corinthians 15:3,4 the elements of the gospel and the promise of Christ and eternal life was not a mystery. That is why it says: “For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures.” However, what was a mystery is the details of how the cross saved sinners, that God can now justify sinners by faith.  That God would dispense his grace in this age to Gentiles apart from Israel and the fulfillment of their promises and through the fall of Israel, from out of all nations the Body of Christ. This is what Paul calls “the mystery of the gospel” in Ephesians 6:19.