How do we know sanctification is important for Christians?

Sanctification is not just a one-time event but a continuous process of spiritual growth and transformation throughout a believer's life. The Reformed understanding emphasizes that while justification is a legal declaration, sanctification relates to the actual moral condition and transformation of the believer. This process is grounded in the work of Christ, as He not only justifies but also sanctifies His people. Through the Spirit, believers are turned from sin, enabled to live righteously, and made increasingly holy. As it is stated in 1 Thessalonians 4:3, this is the will of God, your sanctification, which underscores its importance in the life of a believer.