Mitzvah Kotel Images
On Succot, the Feast of Tabernacles, it is a positive commandment from the Torah in ויקרע [Leviticus 23:40] to gather together the Four Species. “On the first day you shall take the product of hadar trees, branches of palm trees, boughs of leafy trees and willows of the brook, and you shall rejoice before Hashem your God seven days.”
Jewish unity, אחדות, is one of the central themes of Sukkot. The four kinds symbolize four types of Jews, with differing levels of Torah knowledge and observance. Bringing them together represents our unity as a nation - despite our external differences.