[The Holy Spirit] will not do his sanctifying work by the use of his direct divine power. He will only do it by making the glory of Christ the immediate cause of it. This is the only way he works in evangelism, and this is the only way he works in sanctification.
In evangelism the Holy Spirit opens the eyes of sinners to see the glory of Christ who is faithfully preached in the gospel. If Christ is not preached and his glory is not exalted, the Holy Spirit does not open our eyes, for there is no glorious Christ for us to see. The Holy Spirit, we might say, flies in perfect formation be hind the jet of the Christ-exalting gospel. he does his miraculous heart-opening work to make Christ seen and savored as he is preached in the gospel. The Spirit was sent to glorify the Son of God (John 16:14), and He would not save anyone apart from drawing their attention to the glory of the Son in the gospel.
So it is with sanctification. We are transformed into Christ’s image—that’s what sanctification is—by steadfast seeing and savoring of the glory of Christ. This too is from the Lord who is the Spirit. This is the work of the Spirit: to shine the light of truth on the glory of Christ so that we see it for what it really is, namely, infinitely precious. The work of the Holy Spirit in changing us is not to work directly on our bad habits but to make us admire Jesus Christ so much that sinful habits feel foreign and distasteful. My aim here is not to spell this out in detail, but to point it out so that the gospel does its work decisively by revealing the glory of Christ who is the image of God. Therefore, if we neglect the glory of God in Christ as the greatest gift of the gospel, we cripple the sanctifying work of the church.
—John Piper, God Is the Gospel (Crossway, 2005), 91–92.
(HT: The Thirsty Theologian)