Jamieson, Fausset and Brown on 2 Samuel 15:24-25

24-25. Zadok also, and all the Levites ..., bearing the ark--Knowing the strong religious feelings of the aged king, they brought it to accompany him in his distress. But as he could not doubt that both the ark and their sacred office would exempt them from the attacks of the rebels, he sent them back with it--not only that they might not be exposed to the perils of uncertain wandering, for he seems to place more confidence in the symbol of the divine presence than in God Himself--but that, by remaining in Jerusalem, they might render him greater service by watching the enemy's movements.