Sanctification is the gracious work of the Holy Spirit whereby He day by day renews the believer more and more after the image of God.
230. How is the daily renewal accomplished?
The old man, or sin, is put away more and more, and the new man, or the new spiritual life, appears more and more in all our conduct.
Eph. 4:22–24. [R. V.] Put away, as concerning your former manner of life, the old man, which waxeth corrupt after the lusts of deceit;
And be ye renewed in the spirit of your mind,
And put on the new man, which after God hath been created in righteousness and holiness of truth.
231. How does this new conduct appear in the daily life of a Christian?
A Christian denies himself, strives against the devil, the world, and his own flesh; he grows in love toward God and man, and seeks to do the will of God in all things.
Matt. 16:24. If any man will come after me, let him deny himself, and take up his cross, and follow me.
1 Cor. 16:13. Watch ye, stand fast in the faith, quit you like men, be strong.