Paul says that basically there are only two types of thinking and every person thinks according to one of those two ways. There are those who think according to the flesh and there are those who think according to the Spirit. The apostle has been speaking about both groups throughout this letter.
Who are those who think according to the flesh? So far in this letter Paul has mentioned two types of people who fit into this group, and we might be surprised by who they are because initially the two types looked very far apart. The two types are legalism and license. The first marked the Jews who tried to live by God’s laws without his help and the second marked the Gentiles who ignored God’s laws altogether. We could define the first as self-righteous and the second as satisfaction-seeking, and we see both types of people all around us today. There will be very different lifestyles, but one thing marks them all. They are the outcome of thinking according to the flesh.
In contrast, there are those who think according to the Spirit. Who are they? They are those who once were marked by legalism or by license, but who are now marked by faith in Jesus Christ. They chose to repent of their previous lifestyles and to become disciples of Jesus. Since they did so, they have a new way of thinking.
Thinking about the things of the Spirit is a mark of Christian authenticity because it reveals there has been a change in outlook. Those who do so no longer think about what they used to think about. After all, a restored way of thinking is one of the promises of the new covenant in which God says that he will rewrite his laws on the hearts and minds of his people. Moreover, thinking in this new way contributes to Christian assurance – it is one of the evidences that confirm to a person that he is a new creature.
Those who think about the things of the Spirit experience life and peace, and those features are also present and future. What does Paul mean by life? Each believer has spiritual life and others can see it through the various graces that become obvious in his life. As far as peace is concerned, they can know the peace of God that protects their minds and hearts (Phil. 4:7).
So thinking in a way that pleases God leads to his peace protecting our minds which enables us to continue thinking in a way that pleases God which leads to his peace protecting our minds so that we can continue to think in a way that pleases God which leads to his peace protecting our minds, and this process continues on and on.