If this was purely the dream of the man called Paul, then he could write novels or dramas such as no Dickens or Shakespeare ever approximated.
But it was not the dream of Paul; it was the dream of the Father God.
So as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity. (Ephesians 2:15–16)
There was enmity between the Jew under the law and the gentile without the law.
Now that enmity is slain, when the Jew and the gentile are born again, both of them come into the body of Christ, where they are one new man.
This new creation teaching is the master stroke of God.
Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new. Now all things are of God, who has reconciled us to Himself through Jesus Christ, and has given us the ministry of reconciliation. (2 Corinthians 5:17–18)
If God had simply forgiven man for what he had done, and did nothing more, man would continue to commit sin.
But God does not forgive the sinner. He makes him a new creation. He remits and wipes out all that the sinner has ever done. He stops a man being a sinner and makes him a saint by the new creation.
He imparts to him His own nature. Old things pass away. All things become new in Christ.
And put on the new man, that after God hath been created in righteousness and holiness of truth. (Ephesians 4:24 ASV)
This new creation is made out of righteousness, so he is righteousness.
He is made out of holiness, so he is holy.
He is made out of truth, so he is real.
The Father actually unveils His very genius in this new birth.
We are the workmanship of God in Christ Jesus.