What is the relationship between justification and sanctification?

The relationship between justification and sanctification is foundational in Reformed theology. Justification occurs at the moment of faith in Christ when believers are declared righteous before God based on Christ’s finished work (Romans 5:1). In contrast, sanctification is a lifelong process wherein the believer is progressively made holy through the work of the Holy Spirit. This process involves both the act of putting off the old man and putting on the new man, as emphasized by Paul in Colossians 3:9-10. While justification is about the believer's legal status before God, sanctification concerns the believer's moral character and growth in grace, which occurs as they live in light of their justification.