Jamieson, Fausset and Brown on Numbers 9:17

17. when the cloud was taken up--that is, rose to a higher elevation, so as to be conspicuous at the remotest extremities of the camp. That was a signal for removal; and, accordingly, it is properly called (Nu 9:18) "the commandment of the Lord." It was a visible token of the presence of God; and from it, as a glorious throne, He gave the order. So that its motion regulated the commencement and termination of all the journeys of the Israelites. (See on Ex 14:19).