The most significant theological contribution by the late John Murray was his configuration of what he termed “definitive sanctification” (Collected Writings, 2:277-293). Murray doesn’t deny the validity of the traditional definition of sanctification (the Christian’s progressive conformity to the image of Jesus Christ [pp. 294-304]); but he holds that “definitive sanctification” is anterior, and “is the foundation upon which rests [Paul’s] whole conception of the believer’s life …” (p. 279). According to Murray’s exegesis of Rom. 6:1-7:6; 1 Pet. 2:24; 4:1, 2; 1 Jn. 3:6-9 and other Biblical texts, this “definitive sanctification” is the “momentous” and “radical” “transformation” of the believer grounded in his union with Jesus’ death and resurrection, which breaks in him the power of sin and death and resituates him in the sphere of abundant life and radical obedience. This effect of the union ground in past redemptive events is actuated in history when one repents and believes — at that point in history he is definitively sanctified, living as a consequence a life of progressive obedience (sanctification!) with no possibility of apostasy.
I have chosen the word punctiliar to describe the phenomenon. “Punctiliar sanctification” highlights this one-for-all, decisive break with the old man and the world and the flesh and the Devil in those regenerated by the Spirit at a particular point in history. The Bible does not imply that one always knows the precise point at which this personally epochal break occurs in his life, only that it has in fact occurred — the evidence for it is overwhelming (note especially the absolute marks of sonship in 1 John).
This divine act in God’s elect delivers the coup de grace to all merely processional soteriologies — to every notion that one’s security of salvation is held in abeyance until the Final Day. To be sure, God justifies His own at the heavenly tribunal only on the Final Day (Rom. 2:13), and if one has not persevered in good works, he will not be justified — since good works always accompany saving faith (Jas. 2:14-26).
But the finality of the Christian life is proleptically experienced in history in one’s blessed punctiliar sanctification. At that point, despite all the subsequent machinations of Satan and Hell, the believer’s final victory in Jesus is assured (Rom. 8:28-39).
And present, incremental victory over sin — again, despite all the machinations of Satan and Hell — is also assured.
Christian Culture 
Gaffin, Resurrection and Redemption, p124–“Paul characteristically
refers the vocabulary of sanctification not to a process but to a
definitive act occurring at the inception of the Christian life.
Christ has died to sin and lives to God. (Romans 6:10). The plain
implication then is that prior to his resurrection Christ was alive to
sin. Death no longer reigns over HIM…..As long as sanctification is
thought of exclusively as ethical renovation, it will be difficult if
not impossible to understand this element of Paul’s thinking.”
Gaffin, Resurrection and Redemption, p 128—“The view that being
raised with Christ is a metaphor for ‘regeneration’ is an inversion of
Paul’s way of thinking. The counterpart to natural birth is NOT NEW
BIRTH BUT RESURRECTION. If the term ‘regeneration’ is at all
applicable to resurrection, then ‘regeneration’ is the metaphor for resurrection.”