Paul begins this passage by explaining why those who walk according to the Spirit fulfill the Law, while those who are according to the flesh do not. He begins by teaching that those who are according to the flesh set their minds, or commit their minds, to the things of the evil human nature, the flesh. In contrast, those who are according to the Spirit set their minds on the things of the Spirit, which are only good things. The reason for these realities is that a mind set on the flesh is spiritual death, while a mind set on the Spirit is spiritual life, and peace with God. The reason for which the mind set on the flesh is death is that it is hostile toward God. Therefore, it does not subject itself to His law because it is unable to do so, and thus, cannot please God.
In verse 9, Paul reminds his audience that they are not fleshly, but are in the Spirit, or united with the Spirit, if He dwells in them. However, in verse 10, he says that their bodies are spiritually dead because they are sinful, while their spirits are spiritually alive because they possess imputed righteousness. Nevertheless, Paul gives his audience hope in verse 11 by writing that, just as the Father raised Jesus from the dead through the Spirit, He will raise those in whom the Spirit dwells, and give their bodies life.
In verse 12, Paul comes to the conclusion, and the application, of the truths that he has mentioned. The first application is that believers do not have a duty to live according to the flesh because that leads to eternal death. Rather, believers stop committing evil deeds by the Spirit, which leads to eternal life. This shows that they are sons of God because it shows that they are being led by the Spirit. This is true because they have not received a spirit of fear, but a spirit of adoption, which causes them to talk to God as their “Daddy” and “Father.” The reason that they know this is that the Spirit testifies to them that they are children of God. As children of God, they are heirs of God and fellow heirs with Christ if they suffer the same things that He suffered on earth. If they suffer such things, they will be glorified, or given a body like His.