What about this scene is joyful to God?
His people had just returned from captivity, they had just finished rebuilding the walls around Jerusalem in 52 days, and most of them had never heard the law of God!
When they heard the righteous decrees of God for the first time they began to weep because they realized how far they were from what God required! The repentant hearts, the contrite spirits, and the humility of his people is what makes God glad.
Therefore, it was a joyous occasion! Have you made God glad with your repentance? If you have you can find an abundance of strength in the joy of the father!