Sukkot is the Feast of the Lord which is also known as the Feast of Tabernacles (or Booths). According to Leviticus 23:33-43, it is to be a week long celebration of God's provision and a remembrance of how He brought us out of Egypt, and came down to "tabernacle" among us.
When Jesus was born during this Feast, He fulfilled it. Remember He is the Word made flesh, who came down and "dwelt" among us? That word "dwelt" means He pitched His tent among us! HalleluYah!
But that is not all that this Feast rehearses. By keeping it, we not only look back to when He descended on Mt. Sinai to give us His Word, and when He descended and took on a fleshly "tent" to show us how to obey His Word, but we are looking FORWARD to when He will come down to earth again to tabernacle with us, establishing His Kingdom on earth!
Rev 21:2 And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband. Rev 21:3 And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and he will dwell with them, and they shall be his people, and God himself shall be with them, and be their God.
If you would like to learn more about the Feast of Tabernacles, check out the following links:
Short Introductory Video
Feast of Tabernacles/Booths
This is a short video showing how we know when Jesus was born:
The Birth of Messiah