“And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief corner stone;”
King James Version (KJV)
2:20 And are built upon the foundation of the apostles and prophets - As the foundation sustains the building, so the word of God, declared by the apostles and prophets, sustains the faith of all believers. God laid the foundation by them; but Christ himself is the chief corner - stone of the foundation. Elsewhere he is termed the foundation itself, #1Cor 3:11|.
Eph 2:20 Built upon the foundation of the apostles and prophets. They have been built into the temple of the Lord. The word of God, declared by apostles and prophets, is the foundation of their faith, Jesus Christ himself being the chief corner [stone]. The corner-stone was a stone of double size at the corner, which became a part of both walls and joined them together. So he had joined the Jews and Gentiles in the building. He is the foundation-stone on which the building rests, and the stone of union. Compare Isa 28:16 Mt 21:42 Ac 4:11 1Pe 2:7.