Christians fight an ongoing, personal war. This war between the flesh and the Spirit rages until death, and it is a war which gives no quarter. One cannot live both according to the flesh and according to the Spirit. Allegiance must be given to one or the other. Christ’s redemption is not a license to live according to the flesh, as if the flesh had no moral weight anymore. Christ has set us free to walk according to the Spirit, because the flesh no longer rules over us.
Paul begins this oddly short pericope with an admonition: we are debtors, not to the flesh, to live according to the flesh. We owe a debt, without question, but our debt is to God who has given Himself for us. To say that our debt of sin has been paid and that we owe a debt to God are not mutually exclusive ideas. Our unpayable debt of sin has been replaced by the equally unpayable debt we owe to Christ for showing us a wholly undeserved mercy. It is something like a debt of gratitude. If we are willing to show kindnesses and do favors for those who have paid our worldly debts, how much more ought we strive to do what is pleasing to God because of what Christ has done for us!
Yet if we are like indentured servants to God, but serve the will of a different master, what does that say about our allegiances? To live according to the flesh, to receive a spirit of slavery, is to be a son of the flesh, a son of death. The flesh is a merciless master, yet to serve it seems pleasurable. It is never satisfied, yet it always seeks more. “The leech has two daughters: Give and Give. Three things are never satisfied; four never say, ‘Enough’: Sheol, the barren womb, the land never satisfied with water, and the fire that never says, ‘Enough’” (Proverbs 30:15-16). If Sheol, that is, the grave is never satisfied, then how can the tree which bears the fruit of death ever be satisfied either?
However, “if by the Spirit you put to death the deeds of the body, you will live” (Romans 8:13). Through the working and the indwelling of the Holy Spirit, Christians have become the sons of God. They strive against the impulses of the flesh in order to put them to death, not merely to tolerate or even indulge them. The flesh and its ways have no place within the Christian life. To live as if it did is to attempt the impossible, because it means attempting to be the son of two different fathers.
The variety of metaphors which Paul uses to describe this relationship with God should highlight the depth of this mystery. You have changed masters. You have been adopted as sons of the Father. You are debtors of God because of His mercy. You have become the dwelling place of God Himself. To be delivered from sin far exceeds our ability to describe it in human terms, because it is a total and complete change. You have become a new creation. Do not live as if you were not!
Finally, the indwelling of the Holy Spirit provides a greater comfort for us, since the Spirit aids us in our weakness. This indwelling proves that we belong to God, as Paul clearly says in Romans 8:16. But the proofs of this indwelling are not to be found in emotionalism. We know that the Spirit dwells within us because of the fruits of the Spirit. “Every healthy tree bears good fruit, but the diseased tree bears bad fruit” (Matthew 7:17). While such introspection should never be done with the aim of self-glorification and pride, it is not wrong to see the working of the Spirit also in the war we wage against sin. Real patience, for example, is not proud and boastful, but it is also not hidden beyond recognition. The Spirit works, and His work shows itself also in our daily lives.