According to the rambam that says that "he who lives in eretz yisroel all his sins are forgiven," how can a mechalel shabbos ever be killed?!?!?!
levi, brooklyn usa
Although one receives Mechilah with regard to Heavenly punishment, this does not absolve the person from the punishment at the hands of the court, if he is guilty of a sin that warrants such punishment. This is not so unusual; the same applies to Teshuvah. Teshuvah achieves Mechilah from Heaven, but does not exempt from punishments of Beis Din.
In addition, there is a difference between Mechilah and Kaparah (atonement). It is possible that although a person has received Mechilah he may still need to be punished in order to receive a Kaparah.