Albert Barnes Commentary Nehemiah 8:9

"And Nehemiah, who was the governor, and Ezra the priest the scribe, and the Levites that taught the people, said unto all the people, This day is holy unto Jehovah your God; mourn not, nor weep. For all the people wept, when they heard the words of the law." — Nehemiah 8:9 (ASV)

Nehemiah, who is the Tirshatha — Until now, Nehemiah has called himself פחה pechâh (Nehemiah 5:14–15), (Nehemiah 5:18), which is the ordinary word for “governor.” Now for the first time he is called ‘the Tirshatha’ (see Ezra 2:63 note).

The people wept... — Because the Law vividly brought before them their sins of omission and commission. In Nehemiah 8:10, the Jews were not forbidden to be sorry for their sins, but they were only prohibited from marring a festive occasion with the expression of their sorrow.