Summary: This lesson #3 in Ephesians covers the reconciling power of Christ's blood, the salvation of Gentile Christians, the New Covenant, modern day apostles and prophets, and the "mystery of Christ".
Ephesians 2:13-18 But now in Christ Jesus you who once were far away have been brought near through the blood of Christ.  For he himself is our peace, who has made the two one and has destroyed the barrier, the dividing wall of hostility,  by abolishing in his flesh the law with its commandments and regulations. His purpose was to create in himself one new man out of the two, thus making peace,  and in this one body to reconcile both of them to God through the cross, by which he put to death their hostility.
•• “But now in Christ Jesus...”, as opposed to verse 12, which spoke of their former separation from God as unregenerate Gentiles.
•• These Gentile, Ephesian Christians ...
• “once were far away” from God and Christ.
• “But now...have been brought near.”
• “through the blood of Christ.”
••  Jesus, “our peace”, has “made the two one”.
• Jesus destroyed “the barrier” [that is, the law, vs. 15].
• Expositor’s Bible Commentary: “Paul’s language ... here recalls the common rabbinic idea of the law as a fence dividing the Jews by their observance of it from all other races and thus arousing hostility.”
••  “by abolishing in his flesh the law with its commandments and regulations”
• Hebrews 8:13“By calling this covenant ‘new’, he has made the first one obsolete; and what is obsolete and aging will soon disappear.”
• Jesus’ death, burial, and resurrection ushered in a total change of covenants! The Old Covenant became “obsolete”, and the New Covenant, purchased by Jesus’ blood (Luke 22:20), has taken its place.
•• His purpose in doing this? — [15-16] “to create in himself one new man ... reconcil[ing] both of them to God through the cross.”
• “One new man” — that is, the Christian, making no difference if he or she is ethnically Jew or Gentile.
•  Now, through Jesus, “we both [Jew and Gentile believers] have access to the Father by one Spirit.” Now, by the blood of Christ, salvation is available to all!
2:19-22 Consequently, you are no longer foreigners and aliens, but fellow citizens with God’s people and members of God’s household,  built on the foundation of the apostles and prophets, with Christ Jesus himself as the chief cornerstone.  In him the whole building is joined together and rises to become a holy temple in the Lord.  And in him you too are being built together to become a dwelling in which God lives by his Spirit.
••  As a result of the above, Gentile believers are “no longer foreigners ... but ... members of God’s household”.
••  “with Christ Jesus himself as the chief cornerstone”
• 1 Corinthians 3:11“For no one can lay any foundation other than the one already laid, which is Jesus Christ.”
•• [21-22] “In Him” several things happen:
•  “In Him...rises...a holy temple in the Lord.”
•  “In Him the whole building is joined together.”
•  “In Him you too are being built together.”
•  “In Him you...become a dwelling in which God lives by His Spirit.”
3:4b-5 ... 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.
•• The mystery of Christ was not revealed to “men in other generations”, said the apostle Paul. That is a very strong indication that those of whom Paul spoke were contemporary apostles and prophets, alive and receiving that “now” revelation in the early years of the New Covenant. There were New Testament prophets and apostles receiving revelation on earth long after Jesus had ascended back to heaven.
3:6 This mystery is that through the gospel the Gentiles are heirs together with Israel, members together of one body, and sharers together in the promise in Christ Jesus.
•• The “mystery of Christ”  that had been revealed through the Gospel and had “not been made known ... in other generations”  is this :
• That the “Gentiles are heirs together with Israel”.
• Jews and Gentiles are “members together of one body”.
• Jews and Gentiles are “sharers together in the promise in Christ Jesus”.