The mind had to be a controller, and will remain so after the new birth until mind renewal begins to take place. The sin nature had to have mind control over it, the oldman (sin nature) could become compatible with the mind without it, this is what Paul calls a reprobate mind. So with the mind I serve the law of God, Romans 7:25, 25 I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin. This is how they had to serve God and keep the sin nature under control. Through obedience to the law they were keeping the sin nature suppressed, and were pleasing to God. So the law was given to keep the sin nature under subjection to the mind, as long as the law was obeyed. So Christians can stand and rejoice, regardless of the best preaching you have heard, there is no reprobate mind for a believer. So how do we serve God now, in spirit, Romans 1:9, 9 For God is my witness, whom I serve with my spirit in the gospel of his Son, that without ceasing I make mention of you always in my prayers; The birthing (born again experience) makes it possible for the believer now to be renewed in their mind. We do not realize at times how our mind reacts to things such as revelation and instruction from the HolySpirit. Our mind can become an opponent to the things of God, Romans 8:7, 7 Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be. We are trained to read with through doctrinal glasses, reading what we believe to be true. We need to be like Lydia in the book of Acts, with an open heart. We desire the things of God but on the basis of how I understand the scriptures. Understanding can be tricky because most of what you have was given to you by your Father. What He gives you may not be all He has to give, you're understanding is how He keeps you searching, digging in the word, hungering for Him. So you're understanding is very important, but there is a moving on process. Paul had to deal with the Jewish people this way, all they had was their obedience to the law relationship with God, and Paul was trying to take that away. All through Romans he is explaining to them, I have a better way.