“Don’t be dejected and sad, for the joy of the Lord is your strength!”
Nehemiah 8.10c NLT
The people of Israel cried while the words of the law were being read, v. 9. Their sins had caused the destruction of the land. But now they were being restored and it was a time for joy.
The joy the Lord gives and the joy he has in his obedient people makes them strong. Joy comes from the Holy Spirit, 1 Thes 1.6. His power turns sadness into rejoicing.