Albert Barnes Commentary Numbers 33:50-56

"And Jehovah spake unto Moses in the plains of Moab by the Jordan at Jericho, saying, Speak unto the children of Israel, and say unto them, When ye pass over the Jordan into the land of Canaan, then ye shall drive out all the inhabitants of the land from before you, and destroy all their figured [stones], and destroy all their molten images, and demolish all their high places: and ye shall take possession of the land, and dwell therein; for unto you have I given the land to possess it. And ye shall inherit the land by lot according to your families; to the more ye shall give the more inheritance, and to the fewer thou shalt give the less inheritance: wheresoever the lot falleth to any man, that shall be his; according to the tribes of your fathers shall ye inherit. But if ye will not drive out the inhabitants of the land from before you, then shall those that ye let remain of them be as pricks in your eyes, and as thorns in your sides, and they shall vex you in the land wherein ye dwell. And it shall come to pass, that, as I thought to do unto them, so will I do unto you." — Numbers 33:50-56 (ASV)

The expulsion of the Canaanites and the destruction of their monuments of idolatry had already been commanded (see the marginal references); and Numbers 33:54 is substantially a repetition from Exodus 26:53-55. But the solemn warning of Numbers 33:55-56 is new. This was prompted by their past transgressions in the matter of Baal-peor, and by their imperfect fulfillment, initially, of Moses’ orders in the Midianite war.