The four minim (esrog, lulav, hadasim and aravos) represent the unity of the Jewish people. The Midrash teaches that the esrog (which has a good scent and flavor) represents Torah scholars who do good deeds. The lulav has a taste (it grows on a date tree) but it doesn’t have a smell. This denotes the Torah scholars who lack good deeds. Hadasim have a smell, but no taste. They stand for the Yidden who do good deeds, but don’t study Torah. The aravah has neither ascent nor a taste, and they represent the Yidden who lack both qualities.
“Hakadosh Baruch Hu says, ‘Tie them together in one bundle so they will be forgiven for their sins together ” ~VaYikra Rabba 30:12 as quoted by R’ Elemelech Biderman Shlita