What is the meaning of the word "Mishmeres"?
Rashi: It means a charge - any appointment over which is designated to fulfill. 1
Targum Yonasan: "ve'Shamru es Mishmarto" actually refers to the ultimate division of the Kohanim into twenty-four group 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, who, were it not for the Eigel, would have been responsible for matters concerning the Avodah, whom the Levi'im were now being designated to replace.