Joy is something you've got to practice. It doesn't really come naturally to anyone. But if you get the hang of it, it's kind of contagious, and you can infect yourself with joy!
Nehemiah gave the theory of joy. The Levites gave the command to be joyful. But until the people actually went away and practiced joy, they didn't know it. Until they prepared the feast and actually sat down to taste the food, they had no idea how good the feast could be. Until they tasted the drinks, they had no concept of how delightful that could be. And as they followed the instructions to celebrate, they got the hang of the songs. They realized that the Levites weren't kidding, that the day really, really was meant for celebration. They literally practiced joy.
