When Aaron sees that the overking is willing to believe, Aaron understands that what is required is the foundation upon which lies the essential understanding of Jehovah, and especially of the Messiah, who will be Jehovah come to earth. Therefore, Aaron lays out the scriptures. Why begin with the fall of Adam? The requirement for a redeemer was part of the plan that included the fall from Eden. Death of the body and spirit required a redeemer who could remove those two penalties that resulted from the fall.
Since man cannot redeem himself, the Messiah (Jehovah), who will condescend to come to earth, is required to create the redemption. Only this God on earth could rob the grave and reverse the separation from God caused by sin.