Albert Barnes Commentary Nehemiah 8:14

"And they found written in the law, how that Jehovah had commanded by Moses, that the children of Israel should dwell in booths in the feast of the seventh month;" — Nehemiah 8:14 (ASV)

The Feast of Tabernacles had fallen out of practice, either entirely or regarding the dwelling in booths (Nehemiah 8:17), since the time when it was kept by Zerubbabel (Ezra 3:4). It is evident that the observance of the Law, impossible during the captivity, was restored slowly and with difficulty after the return.