When the people were in the wilderness after leaving Egypt, they had to depend on God for their provision. God provided food, water, and didn’t allow their clothes to wear out. The Feast of Tabernacles also celebrates God provision in the past, the present, and looks forward to His provision in the future.
Remembering Their Dependence on God
During the eight days of the Feast of Tabernacles, the people would build three sided structures of tree branches and camp in them. The people would pray, eat, and even sleep in these structures. These flimsy structures are known by many names, tabernacles, booths, shelters, and the Hebrew word Sukkot which simply means tabernacle.
When the nation of Israel was in the wilderness after leaving Egypt, they also lived in flimsy structures or tents. They had to depend on God because there were no crops to harvest and many times there was no water. God provided manna and water from rocks to feed His people.
When the people came into the promised land, they were able to grow crops and harvest them, but they were still dependent on God to provide water and good weather. By the time of the Feast of Tabernacles, all the crops would have been harvested. Barley had been harvested during the time of First Fruits, and wheat had been harvested at the time of Pentecost. Now the olives and grapes were also harvested, and the people gave thanks.
Our Salvation Depends on Jesus
Just as the Jews remembered their dependence on God during the Feast of Tabernacles, we remember that we are dependent on Jesus for our salvation. Ephesians 2: 4 But God is so rich in mercy, and he loved us so much, 5 that even though we were dead because of our sins, he gave us life when he raised Christ from the dead. It is only by God’s grace that you have been saved!… 8 God saved you by his grace when you believed. And you can’t take credit for this; it is a gift from God. 9 Salvation is not a reward for the good things we have done, so none of us can boast about it. 
Any efforts we make to save ourselves are as flimsy as the structures the people live in during the Feast of Tabernacles. God knows that as sinful humans we can’t save ourselves just like the Jews couldn’t feed themselves in the desert. But God is loving and gracious and takes care of the children, both physically and spiritually. His plan was to send Jesus so that when we believe in Him, we can spend eternity with God.
To hear how to depend on God, listen here: