In sanctification, God works in us to make us more Christ-like. It is a process throughout our Christian life on earth where God works to conform us to the image of Christ (Rom. 8:28-29). Throughout our Christian life, we will, by the grace and work of the Holy Spirit, learn to hate and forsake our sins and follow Christ more faithfully. Louis Berkhof defines it thus:
Sanctification may be defined as that gracious and continuous operation of the Holy Spirit, by which He delivers the justified sinner from the pollution of sin, renews his whole nature in the image of God, and enables him to perform Good Works.[13]
Notice that Grudem speaks of “a progressive work of God” and Berkhof of a “continuous operation” which implies that this is not a one-time event like justification.
This work of sanctification is specifically attributed to the Holy Spirit. 1 Corinthians 6:11 says that both justification and sanctification come by the agency of “the Spirit of our God.” Calvin comments on this passage, saying that “Christ, then, is the source of all blessings to us from him we obtain all things; but Christ himself, with all his blessings, is communicated to us by the Spirit. For it is by faith that we receive Christ, and have his graces applied to us. The Author of faith is the Spirit.”[14] 1 Peter 1:2 says that our election was “in the sanctification of the Spirit”. This means that “The election that was purposed by the Father was carried into effect by the agency of the Spirit in making them holy.”[15] Joseph Benson explains the work of the Spirit in the life of the Christian from this passage:
Through sanctification of the Spirit — Through the renewing and purifying influences of the Spirit on their souls; for sanctification implies an internal change wrought in the heart, the first part of which is termed regeneration, Joh 1:13, or a new creation, 2Co 5:17; Tit 3:5; producing, 1st, Power over sin, 1Pe 4:1-2; Romans 6.; over the world, 1Jn 5:4; and the flesh, Rom 8:2. 2d, Devotedness to God and his service in heart and life. 3d, A continually increasing conformity to the divine image.[16]
In 2 Thessalonians 2:13, we are said to be chosen “to be saved, through sanctification by the Spirit and belief in the truth.” A similar idea is given in this passage as in 1 Peter 1:2. It means that believers are “made holy by the Divine Spirit.”[15] This work is “wrought by the Spirit who sanctifies all the elect people of God, first by eternally consecrating them to perfect holiness in Christ, once for all, next by progressively imparting it.”[17] We may lastly add 2 Corinthians 3:18 to the list:
2 Cor. 3:18 And we all, with unveiled face, beholding the glory of the Lord, are being transformed into the same image from one degree of glory to another. For this comes from the Lord who is the Spirit.
It is the Spirit of Christ the ascended Lord Who transforms us into Christ’s image (Rom. 8:29), as we adore and behold His beautiful face through faith. Barnes beautifully explains this passage:
The idea is, that it is by the Lord Jesus Christ, the spirit of the law, the spirit referred to by Paul above, 2Co 3:6, 2Co 3:17. It is done by the Holy Spirit procured or imparted by the Lord Jesus. This sentiment is in accordance with that which prevails everywhere in the Bible, that it is by the Holy Spirit alone that the heart is changed and purified. And the “object” of the statement here is, doubtless, to prevent the supposition that...