4 that the righteous requirement of the law might be fulfilled in us who do not walk according to the flesh but according to the Spirit.
according to the flesh
Paul employed the word “flesh” in different senses in Romans. At times he used it simply in the sense of human nature. At other times he conveyed the idea of sin capacity. The words “according to” mean according to the norm or standard. Non-Christians live their lives according to a standard that is independent of the indwelling Holy Spirit.
but according to the Spirit.
Paul used the word “spirit” in various ways. It can refer to the nature of man, the Holy Spirit, or the new man. The original Greek does not use capitals. The word “Spirit” can mean either the Holy Spirit or the regenerated human spirit, the renewed inward man. Here it means the regenerated spirit of the believer. When the word “spirit” is used in the Greek without the definite article (“the”), as it is in the original manuscripts for this verse here, the term refers to the human spirit or nature.
There is a principle of new life residing within that changes the believer’s orientation. Thus the idea here is to walk according to the norm of the indwelling Spirit of God. The sphere of the believer’s spirit is where the Holy Spirit operates (v. 16).
Non-Christians walk solely according to the horizon and standard of the flesh, but believers walk “according to the Spirit”; that is, they live in a new and unique way because the Holy Spirit indwells them. Christians live by a standard they could never meet on their own strength.
Orientation toward God is an inevitable consequence of the indwelling Holy Spirit in a born-again believer.
Sanctification is an inseparable association of our union with Christ. This is an inevitable consequence of receiving life from the life-giving Spirit. Deliverance from the power of sin is through the death of Christ, but its daily application comes through the power of the Holy Spirit.