On Mitzvot

"Shamor" in Hebrew indicates those actions we may take that has attached them a prohibition (like do not desecrate the Shabbat).  "Zachor" refers to positive commandments, like chanting kiddush on Shabbat.  While the prohibition is punishable, according to the Torah, and the the positive command is not, the rabbis have always referred to the positive commands, mitzvot, as being much greater.  The positive mitzvah is based on love while the prohibition or negative command carries with it penalties.  -Louis Jacobs, based on the Rambam