As soon as man fell, Christ entered on his mediatorial work. Then it was that he began to execute the work and office of a mediator. He had undertaken it before the world was made. He stood engaged with the Father to appear as man’s mediator, and to take on that office when there should be occasion, from all eternity. But now the time was come. Christ the eternal Son of God clothed himself with the mediatorial character, and therein presented himself before the Father. He immediately stepped in between a holy, infinite, offended Majesty, and offending mankind. He was accepted in his interposition; and so wrath was prevented from going forth in the full execution of that amazing curse that man had brought on himself.
It is manifest that Christ began to exercise the office of mediator between God and man as soon as ever man fell, because mercy began to be exercised towards man immediately.
–Jonathan Edwards, from A History of the Work of Redemption; The Works of Jonathan Edwards, Banner of Truth edition, two volume set