Note that chapter 2 is talking primarily to the Gentiles after verse 11.
Prior to that it is talking about our faith in Christ...especially 2:8-9 "for by grace you have been saved through faith, and not that of yourselves, it is the gift of God, not as a result of works, so that no one may boast.
In v 19 Paul continues the message that the Gentiles are now fellow citizens and are of God's household, having been built on the foundation of the apostles and the prophets, Christ Jesus Himself being the cornerstone....
the apostles and prophets, mostly Jewish if I remember, received the message first as noted in verse 11, then it was given to the Gentiles as noted in verse 13. It was given through the blood of Christ. The faith in Christ Paul was writing about in v1-10.
In other words, faith in Christ is the foundation. It is the rock upon which Christianity is built. Nothing else could be the foundation.
1 Corinthians 3:10-11 notes this also. Verse 11 says "for no man can lay a foundation other than the one which is laid, which is Jesus Christ."
Are you a Gentile ? Then by your own admission you must be built on the foundation Ephesians is showing or you are not part of the building. "In other words,", we don't need other words; we have the scripture in front of us; it ties the holy catholic apostolic church together in unity being built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief cornerstone. When you switch the context to 1 Corinthians I note that Paul individualizes the application to each believer: Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you? If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are. Surely each man is not his own church. Do you think Jesus' prayer to the Father failed ? Building upon the Apostles he prayed Neither pray I for these alone, but for them also which shall believe on me through their word; That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me. Something is very seriously amiss with the "Re-formation" and the continual divisions of its aftermath; it is not what the LORD Jesus Christ asked of the Father.