The Obedience of Faith is a chapter-by-chapter, verse-by-verse commentary on the book of Romans. 
 
Below is an excerpt from Chapter 1 on verse 9.
 
9. For God, whom I serve in my spirit This service is not in a superficial, external fashion as under the Law of Moses, but from the heart as of one who had been transformed in his innermost being into the likeness of God. Christianity is a spirit religion. It runs spirit deep. It is not a surface level transformation but one that revolutionizes the very core of our being, our spirit, and works its way outwards from there (Matthew 23:25-26). 
 
in the preaching of the gospel of His Son, The good news is unambiguously good. It is about what God has done and not what we must still do. It is the preaching of Jesus’ work and not our own. It is not to make man more aware of himself and his failures, for that the Law already did. The gospel is to make people aware of Jesus and what He has done. 
 
is my witness as to how unceasingly I make mention of you, This letter flows out of Paul’s prayer life directed towards them. This is a reflection of the concern of God to minister to all those for whom Jesus died. Paul is echoing the concern and the heart of God in his prayers and his desires to reach the whole world with this good news.