Paul describes two groups of people in the world: those who walk according to the flesh and those who walk according to the Holy Spirit who has transformed them. Walking according to the flesh is what we are by nature: fallen and corrupt, with an inclination towards sin. To set the mind means to set the whole course of our direction. To set the mind on the flesh is "death"; a current reality of separation from God. Those who set their mind on the things of the Spirit have the opposite: life and peace. Although there may be fears, they know wonderful comfort.