Sforno on Numbers 7:9/ספורנו על במדבר ז׳:ט׳

1ולבני קהת לא נתן כי עבודת הקודש עליהם, as opposed to what was called עבודת אהל מועד. G’d had commanded concerning these carts that they would form part of what was called עבודת אהל מועד, the task of the members of the family of Gershon and that of the family of Merari. The Kehatites did not transport anything which was part of the actual structure called משכן. They only transported furnishings which were part of the Tabernacle. Those were referred to as מקדש for short. (compare Numbers 10,21 ונשאו הקהתים נושאי המקדש.)