God is our holy Creator and righteous Judge. All people have sinned against him, both in Adam as our corporate representative, and in our own lives individually. That sin deserves eternal death – separation from God in Hell. But God sent Jesus Christ to die the death we deserved for our sin and reconcile us to Him. And He requires that we repent of our sins – turn away from them – and believe in Jesus Christ’s divine righteousness and substitutionary sacrifice. When we do – and only then – God credits us with Christ’s righteousness, and begins to bring our character into conformity with His holiness.