Why do people who are after the flesh mind the things of the flesh?
People after the flesh mind fleshly things because they remain in spiritual darkness, blinded by the God of this world so they cannot believe. Having no concept of the Spirit, they naturally concern themselves only with worldly, material, and fleshly appetites, living according to the old Adamic nature rather than the Spirit.
Les explains that the word 'flesh' here is the same as sin and old Adam. People who are after the flesh are still out in the world, in spiritual darkness, blinded by the God of this world so they cannot believe. Consequently, all they naturally care about are the things of this world; they have fleshly appetites, fleshly vision, materialism, and no concept of the Spirit. So they mind the things of the flesh or the old Adamic nature. By contrast, those who live according to the Spirit—the Holy Spirit with a capital S—mind the things of the Spirit. Les also notes that genuine salvation produces a complete change in lifestyle and desire, so that a person hates what they once loved and loves what they once hated.