Are the prophets in Ephesians 2:20 New Testament prophets, or Old Testament prophets?
It appears from an examination of the context that the prophets mentioned in Ephesians 2:20 were prophets who had been established by God within the New Testament church.
Prior to the coming of Christ, God had dealt exclusively with one physical nation, Israel, as His chosen people. If a Gentile wished to worship the Lord acceptably, he first had to become a proselyte to the nation of Israel. After Jesus’ death and resurrection, the way was opened up for Gentiles to approach God directly through Jesus Christ on the basis of His shed blood, without the necessity of attaching themselves to the physical nation of Israel. This was a marvelous truth that had only been vaguely hinted at in the Old Testament, and that had not been anticipated by Jesus’ followers.
Starting with verse 11 of Ephesians 2, Paul is addressing those Gentile Christians, and explaining how God was creating a new people, composed of both Jews and Gentiles, who would worship Him and make up His household. Paul speaks of this new household as being “built on the foundation of the apostles and prophets, with Christ Jesus himself as the chief cornerstone.” That Jesus would be the cornerstone of this “house,” upon which the apostles and prophets would be added as building blocks, clearly implies that we are reading of a New Testament church.
Further, in Ephesians 3:4-6, Paul speaks of “the mystery of Christ, which was not made known to men in other generations as it has now been revealed by the Spirit to God’s holy apostles and prophets.” This “mystery” was the understanding that Gentiles as well as Jews could become heirs of the promises to Abraham. As noted above, such an understanding did not become known until after the resurrection of Christ and the pouring out of the Holy Spirit upon His followers. Therefore, the “prophets” to whom this “mystery” was revealed would necessarily have had to be New Testament prophets.