D.A. Carson writes:
EVANGELICALS REGULARLY DRAW A LINE BETWEEN JUSTIFICATION AND SANCTIFICATION.
Justification is God’s declaration that an individual sinner is just—a declaration grounded not in the fact that he or she is just, but in God’s accepting Christ’s death instead of the sinner’s, in God’s reckoning Christ’s righteousness to the sinner. It marks the beginning of the believer’s pilgrimage. From the believer’s vantage point, to be justified is a once-for-all experience bound up with God’s good purposes in Christ’s once-for-all death.
By contrast, sanctification in the Protestant tradition has normally been understood to refer to the process by which believers progressively become more holy. (Holy and sanctified/sanctification have the same root in Greek.) This is not a once-for-all experience; it reflects a lifelong pilgrimage, a process that will not be finally complete until the onset of the new heaven and the new earth. It is not what God reckons to us; it is what he empowers us to become.
Failure to distinguish between justification and sanctification frequently ends up with a blurring of justification. If justification takes on a shading of personal growth in righteousness, pretty soon the forensic, declarative nature of justification is lost to view, and we start reimporting some kind of works-righteousness through the back door.
Historically, of course, the warning is well merited. One must always be vigilant to preserve Paul’s emphasis on justification. But the SANCTIFICATION word-group has not always been well-served by this analysis. Those who study Paul have long noted that sometimes people are said to be “sanctified” in a POSITIONAL or DEFINITIONAL sense—that is, they are set apart for God (POSITIONAL), and therefore they already are sanctified (DEFINITIONAL). In such passages the process of progressively becoming more holy is not in view.
Most of the places where Paul talks about being “holy” or “sanctified” fall into this POSITIONAL or DEFINITIONAL camp. That is certainly the case in 1_Corinthians 1:2: Paul writes to “the church of God in Corinth, to those sanctified in Christ Jesus and called to be holy.” The Corinthians already are sanctified; they have been set apart for God. Therefore, they have been called to be holy—that is, to live life in line with their calling (which, by and large, they have been failing to do, quite spectacularly, judging by the rest of the book).
Of course, there are many passages that speak of growth and improvement that do not use SANCTIFICATION; for a start, meditate on Philippians 3:12–16. If we choose to use SANCTIFICATION as a term drawn from systematic theology to describe such growth, we do no wrong. But then we should not read this meaning back into Paul’s use where his focus is elsewhere.