Been meaning to address this, for sometime...
The actual sense of this passage here...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
Which is a part of all this here...
Ephesians 2:11 Wherefore remember, that ye being in time past Gentiles in the flesh, who are called Uncircumcision by that which is called the Circumcision in the flesh made by hands; 2:12 That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world: 2:13 But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ. 2:14 For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us; 2:15 Having abolished in his flesh the enmity, even the law of commandments contained in ordinances; for to make in himself of twain one new man, so making peace; 2:16 And that he might reconcile both unto God in one body by the cross, having slain the enmity thereby: 2:17 And came and preached peace to you which were afar off, and to them that were nigh. 2:18 For through him we both have access by one Spirit unto the Father. 2:19 Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God; 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone; 2:21 In whom all the building fitly framed together groweth unto an holy temple in the Lord: 2:22 In whom ye also are builded together for an habitation of God through the Spirit.
And in all that, the Gentiles are said to have gone from having once been "without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:" verse 12...
To verse 13's "But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ."
Missing within the reading of many of all that there, is the awareness of a change in things between verse 12 and 13 there, that the Apostle Paul does not go into there, but that an Unawareness of, results in a very different sense of all that there, in Ephesians 2.
An unawareness of which also results in a mis-fire on the actual sense of this here...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
Ephesians is Advanced Mystery Truth.
It is a sequel to Romans, and as it's sequel, both builds on, as well also often reiterates various aspects of that Foundational Truth laid out throughout Romans; which is why Paul asserts in Romans chapters 1 and 15 and 16, is he wrote Romans to begin with.
In Romans 1:18-3:20, he lays out how first the Gentiles and then the majority of the Nation Israel BOTH ended up on the wrong side of God's perspective about them.
At the beginning of Romans chapter 3, he briefly touches not only on fact of the existence in Paul's day, of Israel's Believing Remnant, despite the majority of their Nation's fall, but also, on the fact of God's faithfulness to His one day bringing about their Promise.
Paul then goes into much more of all this, in Romans 9-11.
How that despite the fall of the majority of their nation, God is by no means through with what He has purposed to do with, in, and through a Believing Remnant of their Nation, as "a nation" one day.
Which brings us full circle to a fuller sense of what the following passage is actually referring to...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
Verse 12, of Ephesians 2 is referring to how things were for the Gentiles when they were on the outside looking in.
But it also refers to how things had been for Israel before their Nation was "concluded... under sin" with the Gentiles...
Which is why we read in..
Ephesians 2:17 And came and preached peace to you which were afar off, and to them that were nigh.
At this point, the Nation Israel has been concluded as "WERE nigh."
Which is this here...
Romans 3:9 What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin; 3:10 As it is written, There is none righteous, no, not one: 3:11 There is none that understandeth, there is none that seeketh after God.
And which Paul also touches on, in this here...
Ephesians 2:1 And you hath he quickened, who were dead in trespasses and sins; 2:2 Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience: 2:3 Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others.
So, there is all that, and this - which is speaking of a TWO-Fold Purpose - one aspect of concerns the Earth, and another of which concerns things in Heaven...
Ephesians 1:9 Having made known unto us the mystery of his will, according to his good pleasure which he hath purposed in himself: 1:10 That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him: 1:11 In whom also we have obtained an inheritance, being predestinated according to the purpose of him who worketh all things after the counsel of his own will: 1:12 That we should be to the praise of his glory, who first trusted in Christ.
Thus, the sense of this here...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
...is that the foundation upon which those Apostles and Prophets before Paul had based things concerning Israel on - Jesus Christ - is the same chief corner stone upon which the Mystery preached by the Apostle Paul was also based on - on Jesus Christ.
1 Corinthians 3:11 For other foundation can no man lay than that is laid, which is Jesus Christ.
One aspect concerning Christ is in relation to Him as He...
Acts 3:21 Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.
Another aspect concerns Him "according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began," Romans 16:25.
Same foundation for both; different plan, for each.
Acts 17:11,12; Rom. 14:5; Rom. 5:6-8.
The actual sense of this passage here...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
Which is a part of all this here...
Ephesians 2:11 Wherefore remember, that ye being in time past Gentiles in the flesh, who are called Uncircumcision by that which is called the Circumcision in the flesh made by hands; 2:12 That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world: 2:13 But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ. 2:14 For he is our peace, who hath made both one, and hath broken down the middle wall of partition between us; 2:15 Having abolished in his flesh the enmity, even the law of commandments contained in ordinances; for to make in himself of twain one new man, so making peace; 2:16 And that he might reconcile both unto God in one body by the cross, having slain the enmity thereby: 2:17 And came and preached peace to you which were afar off, and to them that were nigh. 2:18 For through him we both have access by one Spirit unto the Father. 2:19 Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God; 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone; 2:21 In whom all the building fitly framed together groweth unto an holy temple in the Lord: 2:22 In whom ye also are builded together for an habitation of God through the Spirit.
And in all that, the Gentiles are said to have gone from having once been "without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:" verse 12...
To verse 13's "But now in Christ Jesus ye who sometimes were far off are made nigh by the blood of Christ."
Missing within the reading of many of all that there, is the awareness of a change in things between verse 12 and 13 there, that the Apostle Paul does not go into there, but that an Unawareness of, results in a very different sense of all that there, in Ephesians 2.
An unawareness of which also results in a mis-fire on the actual sense of this here...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
Ephesians is Advanced Mystery Truth.
It is a sequel to Romans, and as it's sequel, both builds on, as well also often reiterates various aspects of that Foundational Truth laid out throughout Romans; which is why Paul asserts in Romans chapters 1 and 15 and 16, is he wrote Romans to begin with.
In Romans 1:18-3:20, he lays out how first the Gentiles and then the majority of the Nation Israel BOTH ended up on the wrong side of God's perspective about them.
At the beginning of Romans chapter 3, he briefly touches not only on fact of the existence in Paul's day, of Israel's Believing Remnant, despite the majority of their Nation's fall, but also, on the fact of God's faithfulness to His one day bringing about their Promise.
Paul then goes into much more of all this, in Romans 9-11.
How that despite the fall of the majority of their nation, God is by no means through with what He has purposed to do with, in, and through a Believing Remnant of their Nation, as "a nation" one day.
Which brings us full circle to a fuller sense of what the following passage is actually referring to...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
Verse 12, of Ephesians 2 is referring to how things were for the Gentiles when they were on the outside looking in.
But it also refers to how things had been for Israel before their Nation was "concluded... under sin" with the Gentiles...
Which is why we read in..
Ephesians 2:17 And came and preached peace to you which were afar off, and to them that were nigh.
At this point, the Nation Israel has been concluded as "WERE nigh."
Which is this here...
Romans 3:9 What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin; 3:10 As it is written, There is none righteous, no, not one: 3:11 There is none that understandeth, there is none that seeketh after God.
And which Paul also touches on, in this here...
Ephesians 2:1 And you hath he quickened, who were dead in trespasses and sins; 2:2 Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience: 2:3 Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others.
So, there is all that, and this - which is speaking of a TWO-Fold Purpose - one aspect of concerns the Earth, and another of which concerns things in Heaven...
Ephesians 1:9 Having made known unto us the mystery of his will, according to his good pleasure which he hath purposed in himself: 1:10 That in the dispensation of the fulness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him: 1:11 In whom also we have obtained an inheritance, being predestinated according to the purpose of him who worketh all things after the counsel of his own will: 1:12 That we should be to the praise of his glory, who first trusted in Christ.
Thus, the sense of this here...
Ephesians 2:20 And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;
...is that the foundation upon which those Apostles and Prophets before Paul had based things concerning Israel on - Jesus Christ - is the same chief corner stone upon which the Mystery preached by the Apostle Paul was also based on - on Jesus Christ.
1 Corinthians 3:11 For other foundation can no man lay than that is laid, which is Jesus Christ.
One aspect concerning Christ is in relation to Him as He...
Acts 3:21 Whom the heaven must receive until the times of restitution of all things, which God hath spoken by the mouth of all his holy prophets since the world began.
Another aspect concerns Him "according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began," Romans 16:25.
Same foundation for both; different plan, for each.
Acts 17:11,12; Rom. 14:5; Rom. 5:6-8.