Christ's death is relational. He died to propitiate God for our sin and to restore us to right relationship with Him. By faith in Christ, we are declared to be in right relation to the God and Creator of the universe. Unrepentant sin jeopardizes this relationship. That is why repentance is so critical.
Sin is a relational problem.
Repentance is the relational solution. Turn to God. Only He can heal us.