“Sanctification, if it is to spoken of as something other than justification, is perhaps best defined as the art of getting used to the unconditional justification wrought by the grace of God for Jesus’ sake. It is what happens when we are grasped by the fact that God alone justifies. Is is being made holy, and as such, it is not our work. It is the work of the Spirit who is called Holy. The fact that it is not our work puts the old Adam/Eve (our old self) to death and calls forth a new being in Christ. It is being saved from the sickness unto death and being called to new life…
Sanctification is thus simply the art of getting used to justification. It is not something added to justification. It is not the final defense against a justification too liberally granted. It is the justified life. It is what happens when the old being comes up against the end of its self-justifying and self-gratifying ways, however pious. It is life lived in anticipation of the resurrection.
Talk about sanctification is dangerous. It is too seductive for the old being. What seems to have happened in the tradition is that sanctification has been sharply distinguished from justification, and thus separated out as the part of the “salvationing” we are to do. God alone does the justifying simply by declaring the ungodly to be so, for Jesus’ sake. Most everyone is willing to concede that, at least in some fashion. But, of course, then comes the question: what happens next? Must not the justified live properly? Must not justification be safeguarded so it will not be abused? So sanctification enters the picture supposedly to rescue the good ship Salvation from the shipwreck on the rocks of Grace Alone. Sanctification, it seems, is our part of the bargain… The result of this kind of thinking is generally disastrous.
On the level of human understanding, the problem is we attempt to combine the unconditional grace of God with our notions of continuously existing and acting under the law. In other words, the old being does not come up against its death, but goes on pursuing its projects, perhaps a little more morally or piously, but still on its own. There is no death of the old and thus no hope for a resurrection of the new. The unconditional grace of God is combined with wrong theological anthropology. That is disaster… Justification by faith alone demands that we think in terms of the death of the old subject and the resurrection of a new one, not the continuous existence of the old. Unconditional grace calls forth a new being in Christ. But the old being sees such unconditional grace as dangerous and so protects its continuity by “adding sanctification.” It seeks to stave off the death involved by becoming “moral.” Sanctification thus becomes merely another part of its self-defense against grace.”
(From Forde’s essay on sanctification in “Five Views of Sanctification”)