The Jews attacked Midian and killed all the adult males. Moses instructed the soldiers to purify themselves from the ritual impurity that they contracted from their contact with human corpses. Moses’ nephew Eleazar (who had taken over as high priest after his father Aaron’s recent death) instructed the soldiers to purge the eating utensils that they had plundered in battle.
Moses is not Enough
וַיֹּאמֶר אֶלְעָזָר הַכֹּהֵן אֶל אַנְשֵׁי הַצָּבָא הַבָּאִים לַמִּלְחָמָה וגו': (במדבר לא:כא)
Eleazar the priest said to the soldiers returning from battle . . . Numbers 31:21

Ritual defilement is a spiritual condition that surrounds the object, while forbidden food physically penetrates into the object. Thus, a vessel that has absorbed forbidden food needs to be purged of it by being immersed in boiling water or heated until white-hot, whereas a vessel that has been ritually defiled needs only to be immersed in a ritual pool (mikveh), whose waters merely surround the vessel from without.

Moses looked at reality from the higher, Divine perspective. He felt that an overall change in a person’s attitude would affect all aspects of their life, down to the minutest details; therefore, purification from ritual defilement should be sufficient. Eleazar, however, inherited the outlook of his father, Aaron. Looking at reality from the earthly perspective, he knew that sweeping, overall changes are not enough; we must work on the details as well.

Similarly, our inner Moses might tell us that it is enough to correct the past by making sweeping, general resolutions. We must therefore also make sure to listen to our inner Aaron or Eleazar in order to ensure that we take all the necessary steps to purify ourselves of crippling negativity.1