8:12 Because of what God has done for us (vv. 1-11), believers have an obligation to respond appropriately. However we can only do so with the Spirit's help. Paul stated only the negative side of our responsibility here. He could have gone on to say ". . . but to God, to live according to the Spirit."He planned to stress that in the verses that follow.
This verse teaches clearly that the believer still has a sinful human nature within him even though he has died with Christ. God does not eradicate the believer's flesh at conversion. Therefore we must not "live[walk] according to"it. Progressive sanctification is not something the Christian may take or leave. God commanded us to pursue it (cf. 2 Pet. 1:3-11).
8:13 Christians who consistently follow the dictates of the flesh can look forward to death. This cannot be eternal death, separation from God forever, in view of specific promises to the contrary (e.g., vv. 1, 31-39). Therefore it must mean temporal death. Sin produces death in many forms, for example, separation of the body from the soul (physical death that may be premature for those who follow the flesh; cf. 1 Cor. 11:30; 1 John 5:16). It may be separation of the person from others (death in social relationships) or separation of the person from himself (psychological alienation and disorders).
Conversely believers who follow God's will with the enablement of the Holy Spirit and put the deeds of the body (i.e., the flesh; cf. 6:6) to death will experience abundant life. It is possible to possess eternal life and yet not experience it fully (John 10:10). Only Christians who follow God faithfully will experience their eternal life to its fullest potential. This fullness of life involves psychological and social wholeness and well as physical longevity under normal circumstances.
The present tense of the verbs is significant. This tense stresses the necessity of continually putting to death the deeds of the flesh. Paul viewed the presentation of ourselves to God as an initial act of commitment (6:13; 12:1), but He wrote that we must daily and hourly choose to mortify our flesh (cf. 13:14).
"Here is a terrible warning: . . . It is one of the great red lights by which God keeps His elect out of fatal paths. . . .
"For we must note most carefully that a holy life is to be lived by us. It is not that we have any power,--we have none. But God's Spirit dwells in us for the express object of being called upon by us to put to death the doings of the body.' Self-control is one of that sweet cluster called the fruit of the Spirit,' in Galatians 5:22."254
