A comprehensive study of the various additional sacrifices reveals two sets of sacrifices that are connected to two groups of Festivals. The first set refers to the Festivals that fall in the month of Nissan and commemorate the Exodus from Egypt, and the second refers to the Festivals that fall in the month of Tishrei and that mark the beginning of agricultural calendar. The Sukkot Festival ties the two sets together.
A cursory glance at these verses shows that on Sukkot the number of sacrifices brought is double the number brought on the other Festivals. Whereas during all other Festivals, seven lambs are brought, the number doubles to fourteen on Sukkot; only one ram is brought on all the other Festivals, yet on Sukkot two rams are brought.
Why are we commanded to bring a double set of sacrifices on Sukkot? It would appear that Sukkot is a dual Festival. The double nature of Sukkot is a direct reflection of the two sets of sacrifices mentioned above. Sukkot is celebrated both as part of the calendar year that starts in Nissan and as part of the one beginning in Tishrei. Sukkot commemorates the Exodus from Egypt: "in order that your generations should know that I had the children of Israel live in booths when I took them out of the land of Egypt." (Lev. 23:43) At the same time it is also celebrated in the seventh month, Tishrei and is thus a continuation of this second group of Festivals. For this reason, a double set of sacrifices is brought on Sukkot.
This dual nature is also seen in Parshat Emor in which the Festival of Sukkot is listed, followed immediately by a summing up of all the Festivals: "These are the festivals of God, which you shall call as holy convocations." (23:37) This summary is followed immediately by the Torah commanding us a second time to celebrate the Festival of Sukkot: "But on the fifteenth day of the seventh month, when you gather in the produce of the land, you shall celebrate the festival of the Lord for a seven day period." (23:39). The commandment to celebrate Sukkot is mentioned twice because of the dual nature of this Festival.
These two timelines expose us to two fundamental experiences encountered during the Festivals. On the one hand, the Jew faces Jewish history and commemorates events that occurred in the past when God redeemed His people from the slavery in Egypt and gave them the Torah - the calendar year beginning in Nissan. On the other hand, he faces the natural-agricultural experience and prays to his Maker for successful produce. This prayer is made at the beginning of the agricultural year, the month of Tishrei.