We believe that you are misinterpreting the context of the book. It is following the context of what Jesus said to the people in the Sermon on the Mount (Matthew 4:48) "You shall be perfect as your Father in heaven is perfect." When put in context, it means that we should do everything in our power to live in the will of God, and not follow the ways of this corrupted world.
Jesus knew that none of us could be perfect in this physical world, but that we should be rejecting the things that are against God's creation and heavenly intent to the best of our ability. There is no such thing as "cheap grace", but when we make mistakes and fail in our efforts to live as God desires us to live, we are covered by His grace.
In the Love of the Lord,
Frank and Mary