The reason the Jesus came to earth was to pay for our sins.  So what is sin? 
 
Sin (by definition) is - transgression of the law.  By law, it means the moral law of God, as summarily found in the 10 commandments.
 
In Romans 7:7 the Apostle Paul says, “I would not have known sin, except through the law.”
 
In Romans 3:19-20 the Apostle Paul says, “Now we know that whatever the law says, it says to those who are under the law, that every mouth may be stopped, and all the world may become guilty before God. Therefore by the deeds of the law no flesh will be justified in His sight, for by the law is the knowledge of sin.”
 
God’s moral law shows us God’s standard.  When we compare our lives to God’s standard, we see that we have sinned.  Instead of running away from God, we need to look to God’s Son (Jesus) who came to earth, lived a perfect death, died on the cross, and rose again.  We need to look to him for salvation.
 
By trying to be good on our own, we cannot achieve the righteousness that God requires.  We can only achieve this righteousness by repenting of our sins and trusting in Jesus as our only means of salvation.