Definitive and Experiential Sanctification
Definitive sanctification, refers to the the accomplished fact that believers "have been sanctified through the offering of the body of Jesus Christ once for all." (Hebrews 10:10) .. an irreversable event wherein Christ's single offering has perfected for all time those he came to save. This means that our just standing before God can neither be lost nor improved upon. As defined by John Frame, it is "a once-for-all event, simultaneous with effectual calling and regeneration, that transfers us from the sphere of sin to the sphere of God’s holiness, from the kingdom of Satan to the kingdom of God." Definitive sanctification marks us out (or separates us) as God’s chosen people – His treasured and covenantal possession (Acts 20:32; Rom. 1:7; 1 Cor. 1:2; 6:11). So too, definitive sanctification redeems (or frees) us from the dominion (or slavery) of sin by uniting us to Christ, particularly in His death, resurrection and ascension. Sanctification, in this sense, refers to a decisive and radical break from the power of sin.
Experiential sanctification refers to the work of God in and through man which makes us more and more like Christ in our day to day lives/. The Bible declares that as we behold God's glory we are being transformed into the image of Christ from one degree of glory to another. (2 Cor 3:18)." According to John Frame, "We can think of sanctification as the outworking of the new life given in regeneration." It involves the gradual, incremental and (S)piritual work of both putting to death the remains of "indwelling sin" as well as putting on the likeness of Christ. While we work out the salvation given to us, it is God who works in us, both to will and to work for His sovereign good pleasure. (Phil 2:13). We are sanctified in Christ and so our obedience flows from the cross.
"Union with Christ in his death and resurrection is the element of union which Paul most extensively expounds...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 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; 3:1-3). This, then, is the foundation of sanctification in Reformed theology. It is rooted, not in humanity and their 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."
Sinclair Ferguson from Christian Spirituality: Five Views of Sanctification