The entire Christian religion is based around the idea of sin, repayment, and forgiveness. A lot of this hinges on the original sin, which gives an explanation as to why we have free will and are sinners.
But the original sin is a contradiction in itself. The bible states that once Adam and Eve ate from the tree, "then the eyes of both were opened, and they knew they were naked; and they sewed fig leaves together and made loinclothes for themselves." Another account says, "see, now the man has become like one of us, knowing good and evil".
If man did not know what good and evil were before committing the sin, then man could not possibly be at fault. The accounts could even be interpreted as suggesting that we did not have free will in the Garden of Eden, which would mean that the sin was God's.
And that's just in the first chapter of the bible!