The word for etrog relates to the Hebrew root, ragag , which means “to long and desire.” For this reason etrog corresponds to the heart area, the center of conscious emotion and desire.
Etrog is the only one of the plant ingredients that is not indigenous to Israel. It is not one of the famous "seven species" that God used to prove that the Land of Israel is His most prized real estate. This is probably because etrog is not a tree that survives well in arid climates without extensive irrigation. But etrog has its own Biblical distinction—it is singled out as the “fruit of the comely tree.” The proper observance of Sukkot, an important holiday in the Jewish calendar, requires one to purchase a beautiful etrog. Not just an etrog, but a beautiful one. People go from shop to shop looking at hundreds of etrogs on display, trying to find one that meets certain objective standards of beauty and that strikes their particular fancy. This exercise of learning to admire the beauty of a fruit might seem strange, but it heals the soul on a very deep level. The heart's primal sense of aesthetic is cleansed and rectified by this action. And since we want what we find beautiful, the key to correcting our desire nature at its root is to refine our sense of beauty. For these reasons (and more), etrog relates to the heart where, says Kabbala, lies the sefira of Beauty .