Genesis 3:1
Now the serpent was more subtle than any beast of the field which the Lord God had made. And he said unto the woman, Yea, hath God said, Ye shall not eat of every tree of the garden?
Many Christians today believe that the Old testament is not relevant and focus all their attention solely on the New Testament. I believe that the Old testament is especially important as it tells the history of GOD's reconciliation and it all leads up to the Gospel of redemptuon through coming of Jesus Christ.
Genesis 3 tells us of Adam's sin that leads to mankind's fall, so essentially it is the beginning of human history. One man caused the fall and as Paul tells, "For as in Adam all die, even so in Christ shall all be made alive" (1 Corinthians 15:22).
The early Christians, who were mostly gentiles, were guided by the Holy Spirit to incorporate the Old Testament with the New to make the book that is our Bible. So by the Holy Spirit, the importance of both books is revealed.