רַ֤ק הַכֹּֽהֲנִים֙ הָי֣וּ לִמְעָ֔ט וְלֹ֣א יָֽכְל֔וּ לְהַפְשִׁ֖יט אֶת־כָּל־הָעֹל֑וֹת וַֽיְּחַזְּק֞וּם אֲחֵיהֶ֣ם הַלְוִיִּ֗ם עַד־כְּל֤וֹת הַמְּלָאכָה֙ וְעַ֣ד יִתְקַדְּשׁ֣וּ הַכֹּֽהֲנִ֔ים כִּ֤י הַלְוִיִּם֙ יִשְׁרֵ֣י לֵבָ֔ב לְהִתְקַדֵּ֖שׁ מֵֽהַכֹּהֲנִֽים׃
But the priests were too few, so that they could not flay all the burnt-offerings; wherefore their brethren the Levites did help them, till the work was ended, and until the priests had sanctified themselves; for the Levites were more upright in heart to sanctify themselves than the priests.
Read midrashic interpretation of II Chronicles 29:34: and classical rabbinic exegesis.