Steven
E. Runge, High Definition Commentary: Romans
(Bellingham, WA: Lexham Press, 2014), 143-145
Romans 8:12–17
Paul shifts gears in 8:12 from exposition on flesh versus spirit to how we should respond to this information. The Greek has a marker indicating that this call to action is a consequence of what precedes. After contrasting the effects of our minds set on the flesh versus the spirit, Paul now moves on to our obligations in light of God’s Spirit living within us. To reinforce this point, Paul begins in verses 12–13a with what we are not obligated to serve. There are no surprises here, just the direct application of the preceding principles to believers.
In spite of the inherent sin in our flesh and the ongoing battle between sin and the indwelling Spirit of God in our spirit, Paul holds out hope to us. In verse 13b, he specifically describes what happens when we live with our mind set on the spirit, when we allow God free reign in our lives. When we live in such a way, we are doing more than following God—we are simultaneously putting to death the deeds of the flesh. Instead of living in the behaviors that lead to death, we put those deeds to death so that we have life. Only God’s indwelling Spirit enables us to live this way; without His presence, we’d end up being enslaved to sin once again.
When I was growing up, we used to “ditch” people. If someone got completely absorbed in something while we were hiking or hanging out in the hallway at school, the rest of us would quietly sneak off and hide, ditching them. Suddenly the ditched person would look up and find themselves alone. Not very nice, I know. But figuratively speaking, Paul is calling us to ditch our flesh; we should pursue God so avidly, our sinful nature and its desires are left behind. As we pursue God, we are simultaneously putting to death the deeds/desires of the flesh. In fact, we can’t do one without the other.

Fulfilling Your Obligations: Since we have been set free from sin, we are no longer obligated to obey the desires of the flesh. Those who are led by God’s Spirit become heirs of God and put the deeds of the flesh to death.
And just like my ditched friends (or me), our sinful flesh will not be happy. This is why life is an ongoing battle; the flesh is happy when we honor its every whim, but following God means disciplining the flesh. As we pursue God, we are led by the Holy Spirit, and we show ourselves to be sons of God (8:14). This new life in the Spirit is not like the old one; we no longer live in slavery marked by fear.
Paul uses the powerful metaphor of adoption to describe our new life, serving God in His Spirit. Both slavery and adoption involve someone deciding to establish a legally recognized relationship, but the nature of those relationships is radically different. Instead of slavery and fear leading to death, we receive an undeserved intimacy with our Father (8:15). The Holy Spirit’s presence in our spirit provides confirmation of our adopted status (8:16). Note this is the same spirit/Spirit distinction as in verse 4. But this adoption entails much more than being a son or daughter—we also become heirs of all that God has to offer. And as heirs of God, we are also fellow heirs with Christ, His Son. Just as Paul identified us with Christ through His death and resurrection (Rom 6:3–11), he extends that identification to our suffering together and being glorified together (8:17).
If we are to understand the gospel, we must understand its obligations. Being reconciled with God brings us peace—but it also obligates us to turn away from the deeds of the flesh and be led by the Spirit of God instead. Doing so allows us to enjoy our adopted status as God’s sons and daughters. This status not only makes us fellow-heirs with Christ, but also sharers in His suffering. Just as He was glorified by God through His resurrection and ascension, we too can look forward to the day when our fallen flesh and fallen world will finally be redeemed. In the next section, Paul gives us a preview of what lies in store.