Why did God separate and call Paul from his mother's womb?
God separated Paul from his mother's womb and called him by His grace so God could give him the revelation of Jesus the Son, and so Paul might preach Him among the Gentiles. This gospel came by revelation from the ascended Lord, not from men.
Les explains that Paul's apostleship was not received from man or taught by man; it came by revelation of the Lord Jesus Christ. He notes that Jesus Christ was in glory during Paul's revelations, so Paul's doctrine came from the ascended Lord after His death, burial, and resurrection. Until Christ went to the cross and died, He was not the object of faith to the main run of Gentiles. But after He finished the work of the cross and revealed His plan of salvation to this apostle, it became the gospel Paul preached to the Gentiles. Les then points to verse 15: it pleased God, who separated Paul from his mother's womb and called him by His grace, to reveal Jesus the Son and let Paul preach Him among the Gentiles. Paul did not confer with flesh and blood or go up to Jerusalem.
But when it pleased God, who separated me from my mother’s womb, and called me by his grace,
To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood: