Certainly, other Old Testament feasts caused rejoicing. But the Feast of Tabernacles is the only one for which the Lord commands it.
And His people obliged. The rejoicing in ancient Jerusalem during this feast was beyond what we can imagine. The entire city was lit up by the light of just three enormous menorahs, or lampstands. They were so high that priests had to climb ladders in order to tend to the wicks. Live entertainment filled every waking moment that didn't involve worship. Even the famed Gamaliel was known for juggling flaming torches during the celebration!
"Speak to the people of Israel, saying, On the fifteenth day of this seventh month and for seven days is the Feast of Booths to the LORD...and you shall rejoice before the LORD your God seven days." Leviticus 23:34,40b ESV
So what is it about the Feast of Tabernacles that would require a week of exuberant rejoicing? We can look to God's two other commands to shed light on this question.
First, the Lord told the Israelites to live in "booths" for the entire week. These were temporary, makeshift huts with roofs skimpy enough to see the stars through them at night. Living in these temporary tabernacles was intended to remind God's children of His protection and sustenance during their wandering in the wilderness.
God's other command was to celebrate with four specific types of vegetation from the land. Waving them in a special ritual - which is still done today - reminded the people that God alone provided their sustenance, even after they settled in the land flowing with milk and honey.
Live in makeshift huts. Shake some branches. And through it all, rejoice.
The message for God's children then and today is this: Rejoice in all things.
Whether you are wandering in the desert of life or reaping a harvest of blessings, rejoice. You can and you must. Not because times happen to be good, or because you're just putting on a happy face on the outside. We rejoice in all things because - either way - God is sovereign, God is good, and God is there.
God alone is our true shelter and Provider. If we place our trust in Him, nothing can ultimately shake our security. Not a pink slip or a diagnosis or a disappointment. This is how we can find joy in the wilderness and why we find joy in the bounty.
Again, I say, rejoice!