What does God do with the old sin nature when we are justified?

When a person is justified by faith, God reckons the old sin nature dead and gone, declaring the believer just as if he had never sinned. The slate is wiped clean, and the believer now has peace with God through Jesus Christ.

Les explains that justification by faith puts the believer back like Adam was before the fall. God has reckoned the old sin nature dead and gone, and the believer is declared just as if he had never sinned; the slate has been wiped clean. Because of this, the believer has peace with God through the Lord Jesus Christ and is no longer an enemy. The unbeliever cannot experience that peace and lives in turmoil, but the believer can enjoy God's fellowship moment by moment, regardless of behavior, and also has the peace of God (Philippians 4).

Romans 5:1

Therefore being justified by faith, we have peace with God through our Lord Jesus Christ:

How is a person justified before God?

Justification before God is by faith, not by emotional experiences, prescribed rules, or haphazard church membership. What matters is genuine faith in the Gospel and a genuine salvation experience. It is not based on feeling a great emotional upheaval or seeing a great light. This justification means there is now no condemnation.