NUM239 The Levites shall serve in the Beis HaMikdash. It is a king's honor that he has a select group of attendants who are always near to him, serving him on permanent basis. Only those who he chooses personally are allowed to remain so close to him all the time. If every day, someone new were to serve as his personal attendant, and if the group, closest to him changed, it would be a blow to his dignity, for being in his presence is a special privilege that should not be given to just anyone.