The turn around of a zealous follower of Judaism, a rabbi, the star student of Gamaliel, one of the most brilliant students of the Tanahk a defender of the faith. He was a murderer and stanch opponent of the followers of Yeshua, Jesus, Isa.
Yet, in a dramatic turn around, now a follower, a servant, a person willing to die to tell others of the risen, reigning Christ, Messiah, Masih. 
He was taken over by and taken by the Absolute Love. Never to be the same.

Rom 1:1  "Paul, a servant of Christ Jesus, called to be an apostle, set apart for the gospel of God," 

Paul, if he knew anything, he knew the scriptures, It was His whole life, He dedicated Himself to the knowledge and defense of God's written Word. 

Rom 1:2=4  "which he promised beforehand through his prophets in the holy Scriptures, concerning his Son, who was descended from David according to the flesh and was declared to be the Son of God in power according to the Spirit of holiness by his resurrection from the dead, Jesus Christ our Lord, "

Through Jesus Paul personally experienced the grace and the personal mission of bringing the message of loving obedience to those who did not know of God's absolute love, to the nations. This message would change the world. It would bring many to the obedience of faith, for faith in Absolute love changes the very direction of a persons life. A life changed from the appetites of obeying the flesh, to "Desiring God". 
Thank you for the phrase John Piper. 

Rom 1:5-7  "through whom we have received grace and apostleship to bring about the obedience of faith for the sake of his name among all the nations, including you who are called to belong to Jesus Christ, To all those in Rome who are loved by God and called to be saints: Grace to you and peace from God our Father and the Lord Jesus Christ." 

To all of you loved by God, grace and peace to you, from the Absolute Love.