What is sanctification according to the Bible?

Sanctification, as described in Hebrews 10:10, refers to the act of being set apart for holy purposes through the sacrifice of Christ. It is essential to understand that this sanctification occurs 'once for all'—meaning that it is a complete and perfect act achieved by Christ's singular offering. The historic Reformed view emphasizes that sanctification is not gradual but immediate and definitive for all who are elected by God. This doctrine reflects the believer's new identity and status before God as holy, which is not based on their works but solely on Christ's redemptive act on the cross.