The Gospel starts to unfold as early as Genesis 3:15, which says, "And I will put enmity between thee and the woman, and between thy seed and her Seed; (He) shall bruise thy head, and thou shalt bruise His heel." Seven verses later, the LORD God made coats of skins, and clothed them (I would bet my life on those skins being Lamb skins)!
In Genesis 22:1-19, Abraham is described as not only believing the Gospel, he actually acted it out! With Abraham playing the part of God, and Isaac acting in the role of the Son of God, they went to Mount Moriah to offer a sacrifice unto the Lord. Mount Moriah (meaning "the mount chosen by Jehovah") is the original name for what would later become the Temple Mount (2 Chron. 3:1). Golgotha, the "place of the skull," was a part of the mount upon which Jerusalem sits. Isaac carried the wood on his back up the mount (Gen. 22:6), a clear picture of Christ carrying His cross to Golgotha (Jn. 19:17).
While Abraham was told to stop, God did not stop the Roman soldiers, but permitted them to kill His only begotten Son. When one considers the words of God to Abraham, "now I know that thou fearest God, seeing thou hast not withheld thy son, thine only son from Me" (Gen. 12:22), how much more was proven about God's love toward us in the sacrificing of His Son, our Passover Lamb (Jn. 1:29, 36; 3:16; 1 Cor. 5:7; etc.)?!
Because we believe, "perfect love casteth out fear!"