Why?
In the beginning God created man to be in perfect harmony and fellowship with Himself. However, man was deceived by Satan and sinned against God in an effort to be like God; knowing good and evil. God, out of love for His creation, did not abandon them, but instead promised to save His people from their transgressions against Him (Genesis 3:15). Sin came into the world through disobedience and lack of trust in God. As we will see, sin was conquered and paid for through obedience and trust in God. God promised that a son, born of woman, would come and rescue His people from this terrible sin against Him.
The prophesy that God would reconcile the world to Himself was unclear, even Adam and Eve did not know the true extent of the prophesy, because they thought that Cain was the promised child. As time passed God would clarify His prophesy through more prophesy.
Who/What?
The first prophesy to fill in the blanks was in Abraham and Isaac. God had commanded Abraham to offer his one and only son as a sacrifice (Gen. 22:2) to prove that he feared, loved and trusted in God. When Abraham and Isaac reached the place where the sacrifice was to be made Isaac asked where the Lamb was (Gen. 22:7) and Abraham replied,