Passivity is not an option in the Christian life. Though we are eternally free from condemnation in Christ (Rom. 8:1), the New Testament gives us no warrant for inactivity after we put our faith in Jesus. In fact, our work for the Lord begins at the point of conversion, though it does not earn our salvation. Christ merited redemption for us, and we receive His benefits by trusting in Him only (3:21-26). Our spiritual effort is the fruit of the justifying declaration that we are righteous in Christ. God has imputed Christ's righteousness to us through faith alone, and He declares us righteous in Him. The Holy Spirit takes up residence in those who have been justified, and once He has moved in, we work with Him to grow in personal holiness (8:9-11; see Gal. 5:16-26). This is the point of today's passage.
Paul's message in Romans 8:12-13 may seem disturbing at first. Is this passage stating that eternal life rests finally on our sanctification, our growth in holiness? This cannot be, for Paul assures us that everyone justified will be glorified (vv. 29-30). Justification, not our sanctification, secures our glorification, our eternal life in God's presence. Nevertheless, eternal life and sanctification are connected. John Murray, the famous twentieth-century Reformed theologian, explains this in his commentary Romans: "Here is an inevitable and invariable sequence, a sequence which God himself does not and cannot violate. To make [everlasting] life the [end] of life [according to] the flesh would be an inherent contradiction. God saves from the flesh but not in it." In other words, the Lord applies salvation to the believer in an unalterable order. Justification secures our glorification, but sanctification is the road we travel between the two. It would not be fitting to bring people into glory, where they will be perfectly holy, if at their deaths they were still controlled by the flesh—by all that is opposed to God. Thus, although we will not be fully sanctified in this life, the Lord liberates us from the flesh's dominion and sends His Spirit to reside with us and sanctify us in preparation for heaven.
Those ruled by the flesh hate God, having no desire to please Him (vv. 7-8). The last place such people want to be is in His presence. But Christians are no longer bound to the flesh; we are debtors to the Spirit (vv. 12). We want to see the Lord in His holiness. God brings into heaven those who want to be there, and He overcomes our fleshly bondage in regeneration, eliminating our resistance and giving us a desire for Him. Because of that work that is His alone, we are free to work with the Spirit to be readied for life in His presence.
John Murray comments, "The believer's once-for-all death to the law and to sin does not free him from the necessity of mortifying sin in his members; it makes it necessary and possible for him to do so." Our efforts to walk in holiness as we follow the Holy Spirit do not save us, but they show that the Lord has saved us. God is preparing us for heaven, and our calling is to serve Him in the power of the Spirit that we will be renewed and readied for the consummation of His kingdom.