כִּֽי־מִצְוַ֥ת הַמֶּ֖לֶךְ עֲלֵיהֶ֑ם וַאֲמָנָ֥ה עַל־הַמְשֹׁרְרִ֖ים דְּבַר־י֥וֹם בְּיוֹמֽוֹ׃
For there was a commandment from the king concerning them, and a sure ordinance concerning the singers, as every day required.
Read kabbalistic (mystical) interpretation of Nehemiah 11:23: and classical mystical sources.