What was it?
It was the Book of the Law, the Bible of Nehemiah's day, consisting of the five books of Moses.
Slowly and reverently Ezra unrolled the law in the sight of all the people; and they, sitting below, watched him, and as soon as the book was opened they stood up, to show their respect and their reverence for the Word of God.
Then the reading began, and the ears of all the people were attentive to the book of the law.

For no less than six hours Ezra read on, from early morning until midday, yet still the people stood, still the people listened attentively.

There was no stir in the crowd, no one asked what time it was, there was no shuffling of feet, no yawning, no fidgeting; in earnest, fixed attention the people listened.
As Ezra read, a body of Levites went about amongst the crowd, translating what he said.

So long had the people lived in captivity that some of them had forgotten the old Hebrew, or had been brought up from children to talk the Chaldean tongue.

Thus many of Ezra's words and phrases were quite unintelligible to them.