Chapter 13.1, part one

i. They, who are once effectually called, and regenerated, having a new heart, and a new spirit created in them, are further sanctified, really and personally, through the virtue of Christ's death and resurrection, by His Word and Spirit dwelling in them: the dominion of the whole body of sin is destroyed, and the several lusts thereof are more and more weakened and mortified; and they more and more quickened and strengthened in all saving graces, to the practice of true holiness, without which no man shall see the Lord. 

It is characteristic of the Westminster Confession to present biblical doctrines in proper relationship to one another. So here the doctrine of sanctification is introduced with reference to calling and regeneration, as another link in the "golden chain" that stretches from election to glorification.

The phrase "further sanctified" indicates that holiness is intrinsic to regeneration. God's Spirit is a Holy Spirit, after all. So sanctification begins the very moment the Spirit enters a person's life. We are set apart for holiness already in our conversion, when we are given a new heart by the Holy Spirit.

But this is only the beginning. Further sanctification must and does take place, as a progressive work of God the Holy Spirit. The whole Christian life is marked therefore by growth in holiness. Unlike justification and adoption, which as legal declarations take place in a single moment, sanctification gradually unfolds over the course of a believer's pilgrimage. 

The Confession is careful to ground our progressive sanctification in the gospel. On what basis is the believer sanctified? On the basis of the cross and the empty tomb. Progress in holiness is a consequence of the crucifixion and resurrection of Jesus Christ (which is simply the gospel). 

This reality serves to remind us of our ongoing need for the gospel. Our sanctification--no less than our justification--is one result of our Savior's death and resurrection. So hearing the gospel every day does something more than give us the assurance of our faith; it also helps us grow in personal godliness.