Sukkot is a harvest festival. The one mentioned in the Book of Exodus is agricultural in nature – “Feast of Ingathering at the year’s end” (Exodus 34:22) – and marks the end of the harvest time and thus of the agricultural year in the Land of Israel.
Ex 34:22 “Celebrate the Festival of Weeks with the firstfruits of the wheat harvest, and the Festival of Ingathering at the turn of the year. 23 Three times a year all your men are to appear before the Sovereign LORD, the God of Israel. 24 I will drive out nations before you and enlarge your territory, and no one will covet your land when you go up three times each year to appear before the LORD your God. 25 “Do not offer the blood of a sacrifice to me along with anything containing yeast, and do not let any of the sacrifice from the Passover Festival remain until morning. 26 “Bring the best of the firstfruits of your soil to the house of the LORD your God. “Do not cook a young goat in its mother’s milk.” 27 Then the LORD said to Moses, “Write down these words, for in accordance with these words I have made a covenant with you and with Israel.” 28 Moses was there with the LORD forty days and forty nights without eating bread or drinking water. And he wrote on the tablets the words of the covenant—the Ten Commandments.