The etrog has both a taste and an aroma; so, too, do the people of Israel include individuals who have both Torah learning and good deeds.... The date (the fruit of the lulav) has a taste but does not have an aroma; so, too, do the people of Israel include individuals who have Torah but do not have good deeds.... The hadas (myrtle) has an aroma but not a taste; so, too, do the people of Israel include individuals who have good deeds but do not have Torah.... The aravah (willow) has no taste and no aroma; so, too, do the people of Israel include individuals who do not have Torah and do not have good...
Midrash Rabbah, Vayikra 30:11