One very helpful book on the doctrine of progressive sanctification—or how we grow in our display of Christ-likeness—is David Peterson’s Possessed by God: A New Testament Theology of Sanctification and Holiness (IVP, 1995). In a chapter on how we are positionally sanctified in Christ, Peterson makes these two helpful conclusions:
Our essential identity as Christians is formed by Christ and the gospel, not by our own personalities, backgrounds or achievements. Through the death and resurrection of his Son, God has cleansed us from the guilt of sin and liberated us from its consequences and its control. He has set us in a right and faithful relation to himself, together with all who call upon the name of our Lord Jesus Christ. Drawing us into an exclusive relationship with himself in this way, he has made us his holy people, destined to serve him and please him for ever. Sanctification is about being possessed by God and expressing that distinctive and exclusive relationship by the way we live.
Although God calls upon us to express the fact that we have been sanctified by the way we live, our standing with him does not depend on the degree to which we live up to his expectations. It depends on his grace alone. Those who are bowed down by the pressure of temptation and an awareness of failure need to be reminded of the definitive, sanctifying work of God in Christ, by which he has established us as his holy people. On this basis, they should be urged to press on in hope and grasp again by faith the benefits of Christ’s sacrifice. Approaching the exalted Lord with boldness, we may always receive mercy and find ‘grace to help in time of need’ (Heb. 4:16). [pp. 47–48]
This is a very carefully expressed way of explaining how our pursuit of personal holiness is rooted in the finished work in Christ. Without ever coming across as though the Christian is passive in the pursuit of sanctification Peterson makes this point well. He writes in his final conclusions:
The popular view that sanctification is a process of moral renewal and change, following justification, is not the emphasis of the New Testament. Rather, sanctification is primarily another way of describing what it means to be converted or brought to God in Christ and kept in that relationship. It would be more accurate to say that renewal and change flow from the regeneration and sanctification that God has already accomplished in our lives.
Sanctification is thus primarily the work of Christ on the cross and of the Holy Spirit through the word of the gospel, bringing us into an exclusive and dedicated relationship with God, as the holy people of the New Covenant. It is a concept with important, ongoing implications for the church, as well as for individual believers. [p. 136]
Peterson is good at showing how personal holiness is rooted in the finished work of Christ. He also does a fine job connecting personal holiness to (a) the New Covenant promises of God, (b) the broader re-creation of the cosmos, and (c) in showing that growth in godliness is a growth in Christ-likeness in his humiliation and why this should caution us in comparing ourselves to others. These are strong iron beams on which our pursuit of holiness rests.
On progressive sanctification this is not a definitive book (for example Galatians 2:20 is never mentioned!). But nevertheless Possessed by God is very good and deserves a careful read.