Romans 8:12

We are debtors. In view of the saving presence of the Holy Spirit, we are under solemn moral obligations — but certainly not to the flesh — to live according to its dictates. Paul has been explaining that the rule of the flesh results only in death (v. 6). Therefore, the believer need feel under no obligation to his carnal nature. On the other hand, the Spirit of God has brought freedom from the bondage and condemnation of sin (v. 2; ch. 6:22) and now promises eternal life to come (ch. 8:11). This places the ones for whom the Spirit is performing this saving and transforming work, in the position of debtors. They owe everything to the Spirit, and their allegiance and obedience should be wholeheartedly given to this higher power that has entered their lives.

This verse is an answer to those who misunderstand the liberty of the gospel. The gospel frees us from the condemnation of the law and from the destroying error of attempting to keep the law by our own efforts, but it does not free us from obedience to the will of God. It is God’s eternal and unchangeable ordinance that all His creatures should obey Him (see on ch. 3:31). Far from the gospel being the end of obedience, it is but the beginning of real obedience, and Paul describes it as placing us under obligation to obey. If we allow the Spirit of God to have His full way in us, this obligation to obey will not bring any sense of bondage or subservience, rather, we shall ever continue to delight in the law of God (cf. ch. 7:22) as the Holy Spirit gives us power to obey it.

After the flesh. See on vs. 4, 5.