But during the night an angel of the Lord opened the prison doors and brought them out, and said, “Go and stand in the temple and speak to the people all the words of this Life.”
Acts 5:19-20

God gives us liberty for a purpose. We are forgiven so that we can lead others to repentance and eternal life also.

Of course, in order to repent, a sinner must know what he is to repent from, which means "sin", in order to be meaningful, must be defined in a way that doesn't require special knowledge only available to true believers. John's statement that "Sin is violation of the Law" therefore requires that the Law also be objective and understandable by a non-believer.