כִּי־רַבַּ֥ת בַּקָּהָ֖ל אֲשֶׁ֣ר לֹא־הִתְקַדָּ֑שׁוּ וְהַלְוִיִּ֞ם עַל־שְׁחִיטַ֣ת הַפְּסָחִ֗ים לְכֹל֙ לֹ֣א טָה֔וֹר לְהַקְדִּ֖ישׁ לַיהוָֽה׃
For there were many in the congregation that had not sanctified themselves; therefore the Levites had the charge of killing the passover lambs for every one that was not clean, to sanctify them unto the LORD.
Read midrashic interpretation of II Chronicles 30:17: and classical rabbinic exegesis.