וָאֹמְרָ֣ה לַלְוִיִּ֗ם אֲשֶׁ֨ר יִֽהְי֤וּ מִֽטַּהֲרִים֙ וּבָאִים֙ שֹׁמְרִ֣ים הַשְּׁעָרִ֔ים לְקַדֵּ֖שׁ אֶת־י֣וֹם הַשַּׁבָּ֑ת גַּם־זֹאת֙ זָכְרָה־לִּ֣י אֱלֹהַ֔י וְח֥וּסָה עָלַ֖י כְּרֹ֥ב חַסְדֶּֽךָ׃ (פ)
And I commanded the Levites that they should purify themselves, and that they should come and keep the gates, to sanctify the sabbath day. Remember unto me, O my God, this also, and spare me according to the greatness of Thy mercy.
Read Jewish philosophy on Nehemiah 13:22: Rambam's Guide for the Perplexed, Saadia Gaon, and classical Jewish philosophical sources, free online.