Or HaChaim on Numbers 8:6/אור החיים על במדבר ח׳:ו׳

1 קח את הלוים, "Take the Levites! etc." Rashi explains that the word "take!" means by means of words. Apparently Rashi means that Moses was to separate the Levites from the camps of the Israelites and make a separate camp for them seeing the Levites had to guard their ritual purity more than ordinary Israelites. The proof is to be found in the words וטהרת אותם, "and purify them!" Clearly what concerns the Torah at this point is the need for the Levites to maintain a state of ritual purity.