So then, those who are in the flesh cannot please God. (9) But you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His. (10) And if Christ is in you, the body is dead because of sin, but the Spirit is life because of righteousness. (11) But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ from the dead will also give life to your mortal bodies through His Spirit who dwells in you.
The letter to the Romans was written by the apostle Paul and he is addressing the faithful in Rome. The faithful who believe in Christ Jesus belong to Him for time and eternity. They are those who do not walk according to the flesh (natural man) but according to the Spirit – they have been justified by faith in Christ and enjoy new life and peace with God. The unbelieving (those in the flesh or natural man) are hostile toward God and spiritually incapable of trusting Christ for salvation. This human inability is the fundamental fact of theology. Self ruin is possible but self recovery is not. Faith is contrary to the principle of good works.
In verse 9, Paul turns to the faithful who are not in the flesh but in the Spirit. The test of genuine Christianity is the indwelling Spirit; His presence is manifest in the christian behavior and a guarantee of deliverance. We walk in the Spirit but deliverance – sanctification – is a process. The Lord Christ Jesus has delivered believers from spiritual death; our physical body will die because of sin but one day our mortal body will be resurrected through the indwelling Spirit.
The vital thing about faith in Christ is the Spirit has caused us to be born again. The Spirit dwells in every believer and enables them/us to live a holy life (sanctification) and helps us to pray. We want/need to live a holy life which reminds me of Martin Luther who declared “Here I stand. I can do no other.” We strive to behave as we believe.