Celebrate the Festival of Ingathering at the end of the year, when you gather in your crops from the field. (Exodus 23:16b)
So beginning with the fifteenth day of the seventh month, after you have gathered the crops of the land, celebrate the festival to the LORD for seven days; the first day is a day of sabbath rest, and the eighth day also is a day of sabbath rest. 40 On the first day you are to take branches from luxuriant trees—from palms, willows and other leafy trees—and rejoice before the LORD your God for seven days. 41 Celebrate this as a festival to the LORD for seven days each year. This is to be a lasting ordinance for the generations to come; celebrate it in the seventh month. 42 Live in temporary shelters for seven days: All native-born Israelites are to live in such shelters 43 so your descendants will know that I had the Israelites live in temporary shelters when I brought them out of Egypt. I am the LORD your God. (Leviticus 23:39-43)
Though the Feast of Tabernacles (or more properly, Sukkot, or Feast of Booths) fell during the latter harvet or ingathering of crops, it also had a historical purpose. It commemorated the 40 years of wandering Israel did in the wilderness after their refusal to conquer Canaan the first time they arrived there (Numbers 14). Though they lived in tents during that whole time, God provided for their needs and prepared the next generation to take the land.
Coming as it did after the Day of Atonement, it provided a needed celebration of joy after a time of great soul-searching and sorrow over sin. It is one of the three pilgrimage festivals that, like Passover and Weeks, was meant to be celebrated in Jerusalem. Though this is not meant for arguing how much vacation we should have or take, it is interesting that Israelites were called upon to make three pilgrimages which could equal anywhere from 4-6 weeks worth of time traveling and festival depending on how far away from Jerusalem they lived.
Jesus attended a Feast of Tabernacles or Booths incognito one year according to John 7. It was during a time when the opposition of the religious leadership made it very dangerous for him to publically participate. At the opportune moment he revealed himself and made a prophetic proclamation about his authority to speak and the dangers he was facing, then offering living water to whoever wanted it. It is quite possible that prayers were offered at this time for the rains to water the land but Jesus was offering spiritual water for the soul to all who believed in him.
In a sense, we are all living out the Feast of Tabernacles as we await the coming of Jesus to establish his kingdom. We are in the wilderness, so to speak, in a temporary arrangement for living that will be done away with when the perfect or complete comes.
For further reading: http://www.christcenteredmall.com/teachings/feasts/tabernacles.htm, http://www.nowpublic.com/culture/sukkot-2010-feast-tabernacles-or-building-fort-2677107.html, http://www.jewfaq.org/holiday5.htm, http://www.answers.com/topic/sukkot, http://www.bookrags.com/wiki/Sukkot