Israel received the command to make war upon the Midianites at the same time as that to fight the Moabites, but whereas Moses at once waged war against Midian, it was not until David's time that a relentless war was waged against Moab. There was several reasons why the Midianites were to receive their punishment before the Moabites. Firstly, Moab's hatred against Israel was not quite without foundation, for although the Israelites had not attacked them in war, still they had inspired them with great fear by pillaging the Moabite region, hence the Moabites tried by every means to be rid of Israel.
Midian, on the other hand, had no cause for undertaking hostilities against Israel, and yet they not only joined the Moabites, but outdid them in their hatred against Israel. Furthermore Moab wanted to kill Israel, but Midian wanted to tempt them to sin, which is worse than death. The delay in punishing Moab also corresponded in other ways to God's plan, for the Moabite Ruth was destined to become the mother of the dynasty of David, hence God said to Israel: "Wait yet a while in this matter of the war against the Moabites: I have lost something valuable among them. As soon as I have found it, ye shall avenge yourselves of them."