What is the meaning of the word "Mishmeres"?
Rashi: It means a charge - any appointment over which is designated to fulfill. 1
Targum Yonasan: "v'Shamru es Mishmarto" actually refers to the ultimate division of the Kohanim into 24 groups who would serve in rotation in the Beis-ha'Mikdash.
Rashi: As we find in connection with Bigson and Teresh (See Megilah, 13b).
What is "Mishmares Kol ha'Eidah" referring to??
Seforno It is referring to the Sanhedrin. If not for the Eigel, they would have been responsible for matters concerning the Avodah. The Levi'im were now being designated to replace them.