Sin is purposely disobeying God. The consequences of sin are many, not the least of which is damage to one’s relationship with God. Fortunately, God has forgiven our sins. He demonstrated His love for us by dying for all, providing a way to be freed from the bondage of sin.
The Bible explains that we have all been created in God's image, but that His image in us has been damaged by sin. This seems evident when we look at the world around us. Some, however, find it offensive to hear that they are sinners.