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!
It didn't take long for them to get used to joy - and it doesn't take long for us, either. Joy is contagious, and even a baby can teach joy to adults. Haven't you seen it? A baby smiles, or laughs, and every adult who sees it smiles and laughs in return.
Would you like to learn to play the piano? It'll take practice. Want to be an artist? Prepare to practice the basic strokes. Want to become proficient at anything? You'll have to start out as a rookie, learn the basics, and then practice. As it is with a musical instrument, it is with joy. The more you practice, the better the music.
Maybe your goal is to join a gym and get in shape. Obviously, one single day in the gym isn't going to get the job done. You'll need to do a little bit, every day, get a schedule, and stick to it.
Or perhaps it's nutrition that is your thing. A year from now, it'll be hard to remember a single meal. But a balanced diet will bear long-term benefit - as long as you practice it.
Now, the Bible comes along and says: "Practice joy!"
If you can practice joy in the midst of lean times, you'll move quickly from "surviving" to "thriving.