“Union with Christ in His death and resurrection is the element of union which Paul most extensively expounds. But the principle of Romans 6 is a wider one: if we are united to Christ, then we are united to Him at all points of His activity on our behalf.
We share in His death (we were baptized into His death), in His burial (we were buried with Him by baptism), in His resurrection (we are resurrected with Christ), in His ascension (we have been raised with Him), in His heavenly session (we sit with Him in heavenly places, so that our life is hidden with Christ in God) and we will share in His promised return (when Christ, who is our life, appears, we also will appear with Him in glory (Rom. 6:14; Col. 2:11-12; 3:1-4).
This, then, is the foundation of sanctification in Reformed theology. It is rooted, not in our humanity and our achievement of holiness or sanctification, but in what God has done in Christ, and for us in union with Him.
Rather than view Christians first and foremost in the microcosmic context of their own progress, the Reformed doctrine first of all sets them in the macrocosm of God’s activity in redemptive history. It is seeing oneself in this context that enables the individual Christian to grow in true holiness.
This general approach is well illustrated by Paul’s key statements: ‘We know that our old self [anthropos, man] was crucified with [Christ] in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin’ (Rom. 6:6).’
What is here said to be accomplished already is the central element in sanctification (we are no longer slaves to sin, we are servants of God). It is accomplished by doing away with ‘the body of sin’– an expression which may refer in the context of Romans 6 to the physical body, or more generally, to bodily existence as the sphere in which sin’s dominion is expressed.
In Christ, sin’s status is changed from that of citizen with full rights to that of an illegal alien (with no rights– but for all that, not easily deported!). The foundation of this is what Paul describes as the co-crucifixion of the old man with Christ.
The ‘old man’ (ho palaios anthropos) has often been taken to refer to what I was before I became a Christian (‘my former self’). That is undoubtedly implied in the expression.
But Paul has larger canvas in mind here. He has been expounding the fact that men and women are ‘in Adam’ or ‘in Christ’. To be ‘in Adam’ is to belong to the world of the ‘old man’, to be ‘in the flesh”, a slave to sin and liable to death and judgment.
From this perspective, Paul sees Jesus Christ as the second man, the last Adam, the new man. He is the first of a new race of humans who share in His righteousness and holiness. He is the first of the new age, the head of the new humanity, through His resurrection (compare 1 Cor. 15:45-49). By grace and faith we belong to Him.
We too share in the new humanity. If we are in Christ, we share in the new creation (2 Cor. 5:17), we are no longer ‘in the flesh’, but ‘in the Spirit’ (Rom. 8:9). The life and power of the resurrection age have already begun to make their presence felt in our life.
What is so significant here is the transformation this brings to the Christian’s self-understanding. We do not see ourselves merely within the limited vision of our own biographies: volume one, the life of slavery in sin; volume two, the life of freedom from sin.
We see ourselves set in a cosmic context: in Adam by nature, in Christ by grace; in the old humanity by sin, in the new humanity by regeneration. Once we lived under sin’s reign; now we have died to its rule and are living to God.
Our regeneration is an event of this magnitude! Paul searches for a parallel to such an exercise of divine power and finds it in two places: the creation of the world (2 Cor. 4:6; 5:17) and the resurrection and ascension of Christ (Eph. 1:19-20).
Against this background Paul urges radical consecration and sanctification (Rom. 6:11-14). In essence his position is that the magnitude of what God has accomplished is itself an adequate foundation and motivation for the radical holiness which should characterize our lives.
In actual practice, it is the dawning of this perspective which is the groundwork for all practical sanctification.
Hence Paul’s emphasis on “knowing’ that this is the case (Rom. 6:3, 6, 9), and his summons to believers to ‘consider’ themselves dead to sin and alive to God in Christ Jesus (Rom. 6:11).
‘Consider’ (‘reckon’, KJV) does not mean to bring this situation into being by special act of faith. It means to recognize that such a situation exists and to act accordingly.
Sanctification is therefore the consistent practical outworking of what it means to belong to the new creation in Christ. That is why so much of the New Testament’s response to pastoral and personal problems in the early church was: ‘Do you not know what is true of you in Christ?‘ (Rom. 6:3, 16; 7:1; 1 Cor. 3:16; 5:6; 6:2, 3, 9, 15, 19; 9:13, 24).
Live by the Spirit’s power in a manner that is consistent with that! If you have died with Christ to sin and been raised into new life, quit sinning and live in a new way.
If, when Christ appears, you will appear with Him and be like Him, then live now in a manner that conforms to your final destiny!”
–Sinclair Ferguson, “Christian Spirituality: The Reformed View of Sanctification,” in Some Pastors and Teachers (Carlisle, PA: Banner of Truth, 2017), 534-536.