Set Apart for God

"You are . . . a holy nation" (1 Pet. 2:9).

Holiness involves the decreasing frequency of sin and the increasing frequency of righteousness.

Christians are a holy nation—a people set apart from sin and hell to an intimate relationship with God. Originally Israel was God's holy nation, but by unbelief she forfeited that privilege. Now the church, which consists of both Jew and Gentile, is His unique people, and will remain so until the nation of Israel repents and receives her Messiah at His return (Zech. 12:10).
Biblical holiness (sanctification) is often misunderstood, but it needn't be. When the Holy Spirit delivered you from the domain of darkness and transferred you into the kingdom of Christ, you became His special possession. That doesn't mean you're sinlessly perfect, but it does mean you're no longer a slave to sin, the devil, and death. That's positional sanctification. Practical sanctification is the decreasing frequency of sin and the increasing frequency of righteousness as you progress in your Christian walk.
Sanctification should not be confused with false standards of holiness, adopted by those who, like the Pharisees, attempt to be holy through external means; or, like the Stoics, have a passionless devotion to duty; or, like monks, isolate themselves from the world; or, like the quasi-Christian psychologists, replace sanctification with introspection, self-analysis, and improvement of one's self-image.
True holiness begins with a love for Christ Himself. That's what compels you toward greater sanctification. Peter said that you were "chosen according to the foreknowledge of God the Father, by the sanctifying work of the Spirit, that you may obey Jesus Christ" (1 Pet. 1:1-2). Christ Himself became to you "wisdom from God, and righteousness and sanctification, and redemption" (1 Cor. 1:30). In Him you were saved, which is the beginning of sanctification, and in Him you have every resource necessary for progressing in holiness.
Suggestions for Prayer

Thank God for your positional holiness in Christ, for by it you are perfect in His sight.

Thank Him for the Spirit's power in your life, which enables you to live in a manner pleasing to Him.

For Further Study
What do these passages say about sanctification: Acts 15:7- 9, 1 Thessalonians 4:3, Hebrews 10:14, and 1 Peter 1:15-16?