Nobody really wants to take the blame for what they did, do they? Adam and Eve both know they've done wrong, and yet they find someone else to blame. As MacArthur says, it is a 180 degree change in their attitude towards God caused by ONE sin. ONE sin and they are instantly changed forever.
Rather depressing, isn't it? And though God knew they had sinned, He already KNEW, He came looking for them anyway.
That is the hope in this hopeless story. Despite our sins, despite our failings, God comes searching for us. He still desires a relationship with us.
All we have to do is repent, turn our back on the sin in our lives, and turn to God.