“Thereafter, the sons of Kehat shall come to bear…” – Moses said before God: Is the blood of the sons of Kehat safeguarded and the blood of the sons of Aaron unprotected? The Holy One blessed be He said to him: No; rather, Aaron is of the most sacred order, as it is stated: “Aaron was set apart to sanctify him as of the most sacred order” (I Chronicles 23:13), and the Ark is of the most sacred order.
The most sacred order does not harm the most sacred order. However, the sons of Kehat are not of the most sacred order, but the Ark and all the vessels situated within are of the most sacred order, and they harm them. Therefore, the sons of Aaron must direct their attention so that the sons of Kehat will not die. “These are the burden of the sons of Kehat in the Tent of Meeting” – these are borne, but the rest of the vessels are not borne, but rather are in wagons.
Likewise it says: “But to the sons of Kehat he did not give, [because the sacred service is upon them; they shall bear on the shoulder]” (Numbers 7:9).