When the Children of Israel left Egypt, the Lord had them stay in Succoth—temporary dwellings. As a reminder of the miracles that had happened to them in the desert, during the Exodus, The Children of Israel are commanded each year to leave their homes and dwell in Succoth for seven days. They are also commanded to make blessings on the Four Species: datepalm branches, myrtle, willow, and citron.
During Succoth the souls of the seven shepherds of Israel—Abraham, Isaac, Jacob, Moses, Aaron, Joseph, and King David—actually leave Gan Eden to partake in the divine light of the earthly Succoth. These are called Ushpizin (“holy guests”). Similarly, it is considered a blessing to host guests in the Succah.