The law of Moses was rediscovered. There are a lot of details in this chapter which bear mentioning. Notice that Ezra is described as the scribe and Nehemiah as the governor of the land. We consider them prophets, or people who are proclaiming the Word of the Lord. Once the law of the Lord is discovered notice how there is a public reading of it. There are also people strategically placed who can interpret or help the people understand what is being read.
The reaction to what is being read is one of grief because they recognize that they are not following the law as they ought to follow it. They recognize that in order to obey God they simply need to be doing things differently, and it makes them grieve because they know that they have let God down. But the order from Nehemiah is that they not be grieved but rather go home and eat the fat off the land and drink wine and celebrate, because the joy of the Lord is our strength. I love that song. Find it below.
As a result of finding the law they also rediscover some of the festivals that they should be celebrating, like the festival of booths. The festival of booths is that festival that they were celebrating when Jesus enters Jerusalem on a donkey, what we call palm Sunday. You can read in this chapter why they would have branches available, because they were living in booths made from branches. So the people of God were redirected in their lives because they were exposed once again to the law of the Lord. See what happens when you read Scripture and take it seriously?