Christ's death on the cross was for my Sin. But the far greater glory is that Sin could not hold Christ dead. Death can only hold anyone with sin. So, after being heaped up and covered over with all the sins of the world, death hung on, but came to the final payment for the final sin and fell off of Christ, and Christ, the sinless sacrifice arose and lives and reigns with His Father for eternity.
God imputed onto Christ, His sinless son, all the sins committed by man.
Because of Christ's obedience to the Father, His Righteousness is imputed to me through my faith in Him. God's work in me is to impart Justification unto me not because I am sinless, but because of the Atonement bought through blood of Christ.
Sin doesn't just go poof but has to be atoned for and that is only found in the 2nd Adam, Jesus Christ, who is sinless. In Christ's blood God is able to cover/erase our sin, making us righteous, pardoned, a new creature in Christ, born again.
I can be Justified, declared Righteous, FREE through Jesus Christ