The parasha’s account of the war with Midyan forms the background for the laws of tevillat keilim (immersion of utensils). Bnei Yisrael acquired spoils, including food-related utensils. Moshe taught: "Whatever goes into fire shall be passed through fire and be purified, but in the waters of niddah it shall be purified" (Bamidbar 31:23). Firstly, one has to kasher the utensils in which forbidden foods were cooked so they can be used for kosher foods. Secondly, there is a mitzva to immerse the utensils in a mikveh before using them. What is the idea behind this tevilla?
The Rambam writes: "This tevilla done to utensils of meals that are obtained from a non-Jew and afterward they become permitted for eating and drinking is not related to purity and impurity but is from the Rabbis, and it is hinted in, ‘Whatever goes into fire...’" (Maachalot Assurot 17:5). A few halachot later, he writes: "There are other things that the Sages forbade, even though there is no source in the Torah, in order to distance oneself from non-Jews before one mixes in with them and come to intermarriage, and these are them: not to drink with them even when one does not have to fear wine used in idol worship, and they forbade eating their bread and their cooked foods even when one does not have to fear that they come from pots that have absorbed non-kosher" (ibid.:9).
According to the Rambam, the requirement of tevillat keilim is also to battle assimilation. Most Rishonim see tevillat keilim as a mitzva from the Torah but one that teaches the concept of not allowing relationships between Jews and non-Jews to deepen. By restricting eating and drinking with non-Jews and even with related utensils, the danger of the setting of joint eating is lessened. This served as a model for a slew of rabbinic initiatives that are intended to curb assimilation. We will mention a few.
1) Eiruv chatzerot - Even within fenced-in areas, we must "rent non-Jews’ domain" before being able to carry there. This process was intended to make joint living quarters with them more difficult. 2) One may not eat bread that was baked in a non-Jew’s home irrespective of kashrut issues. 3) One may not eat important foods cooked by a non-Jew. 4) One may not drink wine along with non-Jews irrespective of kashrut problems. 5) The Rabbis tried (unsuccessfully) to forbid use of non-Jews’ oil.
This partial list demonstrates the Rabbis’ great fears of intermarriage/assimilation, which endanger the Jewish nation’s survival. Nowadays assimilation is eating into huge parts of our people, reaching 90% in some places. Our survival after millennia of exile is a historically unprecedented open miracle. Our parasha teaches us that while we have to thank Hashem for the miracle, we also have to take our own concrete steps, with our Rabbis’ laws’ help, to stem the tide of assimilation.