Sforno on Numbers 3:7/ספורנו על במדבר ג׳:ז׳

1משמרת כל העדה לפני אהל מועד לעבוד את עבודת המשכן, to assist in the tasks needed to perform the service in the Temple properly. Had it not been for the sin of the golden calf, it would have been the duty/privilege of the members of the Supreme Court, Sanhedrin, to carry out the tasks now allocated to the Levites.