Ephesians 2:20 because you have been built on the foundation of the apostles and prophets, with Christ Jesus Himself as the cornerstone. 21 In Him the whole building, being joined together, grows into a holy temple in the Lord, 22 in whom you also are being built together into a dwelling place of God in the Spirit. NET
Jesus is the cornerstone with the foundation of understanding being the prophets and the apostles. Typically this reference would refer to the Old Testament prophets and the New Testament apostles which is how it applies here. (The Jewish people divide the Old Testament into three parts: the law, the prophets and the writings). This stands to reason since our understanding of the Messiah comes from the Old Testament prophets.
This same wording will appear a few verses from now in chapter 3 with a different meaning for “prophets”. During this time, there are prophets within the church saying “thus saith the Lord” as God communicates through the apostles and prophets in the apostolic church. (Both of these groups have had this mystery revealed to them). Prophets have fallen out of favor today because of the possibility of undermining Scripture but Paul tells us in Thessalonians not to despise the prophecies but to test them.
Ephesians 3:1 For this reason I, Paul, the prisoner of Christ Jesus for the sake of you Gentiles – 2if indeed you have heard of the stewardship of God’s grace that was given to me for you, 3 that by revelation the divine secret was made known to me, as I wrote before briefly. NET
Looking ahead, Paul will start verse 14 with this same phrase (“For this reason”). Paul wants to talk about prayer here but gets temporarily sidetracked before taking this up again at verse 14.
Paul was in prison a couple of times with this being one of the epistles written while he was jailed. He was in prison because he had allegedly brought a Gentile into the Temple. (See Acts 21). The wording at verse 2 is a little odd as by now, most would know who Paul is. On the other hand, Paul has been away from this church for a long time and there could well be many new members who have no idea who he is.
In chapter two, grace refers to salvation. Grace as used here refers to the spiritual gifts given to Christians for ministry as pastors, evangelists, prophets, and teachers. In Paul’s case, Christ didn’t just knock him off his donkey in Damascus as a means of converting him to Christianity but also to call him to be an apostle. (see Galatians 1 and 2 or Ephesians 4:11 for spiritual gifts).
Ephesians 3:3 how that by revelation the mystery was made known to me, as I wrote before in few words, 4 by which, when you read, you can perceive my understanding in the mystery of Christ; NHEB
1Thessalonians 2:13 And we continually thank God because, when you received the word of God that you heard from us, you accepted it not as the word of men, but as it truly is, the word of God, which is also now at work in you who believe. BSB
This is why Paul’s writings are called Scripture. They aren’t just the thoughts of a man trying to be a good Christian but rather they are the revelation of God to Paul. God has told him and shown him things that wouldn’t be known had they not been revealed. Paul’s ministry is based upon this revelation. (Recall that in Ephesians 1:9-10, we see that this mystery of God’s will is to unite all things in Christ).
Ephesians 3:5 which in other generations was not made known to people, as it has now been revealed to his holy apostles and prophets in the Spirit; 6 that the non-Jews are fellow heirs, and fellow members of the body, and fellow partakers of the promise in Christ Jesus through the Good News, NHEB
While the same Greek word is translated both here and in Ephesians 2:20 as “prophet”, it doesn’t have the same meaning here. Things have changed because now there has been a revelation made to us of something that was not clear to the earlier people in the Old Testament. Think, for example, of Jonah and the resistance to the idea that God would care anything at all about the Gentiles. Paul is saying that this is something that wasn’t well understood back then.
Ephesians 3:7 I became a servant of this gospel according to the gift of God’s grace that was given to me by the exercise of His power. 8 To me – less than the least of all the saints – this grace was given, to proclaim to the Gentiles the unfathomable riches of Christ NET
The grace here is a spiritual gift as Paul is an apostle because of God’s grace and power. All Christians have received the gift of grace but also a gift to be used in sharing this message. The power language is particularly important in Ephesus because it is a city filled with the occult.
After teaching the apostles that they will be baptized with the Holy Spirit in Acts 1:5, Jesus tells them a few verses later that they will receive power when the Holy Spirit comes upon them. Paul is always overwhelmed by the grace he received as he was an unlikely candidate for the job of apostle to the Gentiles. No one was likely more surprised than him by this appointment from God.
Hebrews 2:3 how will we escape if we neglect such a great salvation? It was first communicated through the Lord and was confirmed to us by those who heard him, 4 while God confirmed their witness with signs and wonders and various miracles and gifts of the Holy Spirit distributed according to his will. NET
As the truth of the Gospel is proclaimed, it is accompanied with signs and wonders that attest to that truth. Peter knew who Jesus was because of the signs and wonders. With so many people making religious claims in Ephesus, the average person in Ephesus might wonder why they should listen to Paul rather than someone else. Paul’s answer is because of the power.