Sin produced a separation between God and man. It broke the Covenant of Works and destroyed the relationship of peace, friendship, and communion which man had with God in Paradise.
From man's side, no restoration of relationship (of fellowship and favor) with God was possible. God is perfectly holy and righteous - He cannot tolerate sin. The Lord is also perfectly true - He cannot lie. God had said, "In the day thou eatest thereof (from the Tree of the Knowledge of Good and Evil) thou shalt surely die" (Genesis 2:17b). Man's original and actual sin makes deliverance by man impossible.
What is impossible by man, however, is possible with God! God graciously provided a perfect mediator, One through whom God and man could be fully reconciled. This mediator is the Lord Jesus Christ. As the second Adam, as the head of the Covenant of Grace, He provided full satisfaction and payment for man's sin.
Scripture speaks of, and pictures, Christ's work as mediator in numerous passages. The following is one example:
Restoration - The state of being re-established or brought back to the former condition
Mediator - One who attempts to bring two disagreeing parties into agreement
Reconciled - Agreed; settled; restored union and friendship after separation