Because their office was to wait on the sons of Aaron
 The priests: 
 for the service of the house of the Lord;
 to assist them therein, and not to bear burdens as in times past; the Targum is, 
``wherefore the place of their habitations was by the side of the sons of Aaron, for the worship of the sanctuary of the Lord:''in the courts, and in the chambers, and in the purifying of all holy