The sequence of the pesukim raises two issues. First, the order of the commands demands explanation. One would assume that the admonition regarding subtracting from the Torah would be written first, because it is so obvious. The Torah should have subsequently warned us against trying to become too pious to the point that we feel we know what the Creator is thinking.
Horav Dovid Feinstein, Shlita, explains that in truth the “do not subtract” is essentially a corollary of the “do not add.” Whenever one attempts to amend the Torah by adding to it, he is actually subtracting from it. In effect, he is inferring that the Torah is not as complete as it should be. He feels it needs just a little more. Thus, by adding, the individual is challenging the perfection of the Torah.
Second, equating these prohibitions with the sins committed at Pe’or suggests a more intricate relationship between the two. At Pe’or, a significant number of Jews sinned with the Midianite women, while others actually worshipped the pagan idol, Pe’or. Horav Moshe Shternbuch, Shlita, suggests that an individual who amends the Torah by adding “new” mitzvos in order to enhance his sanctification of Hashem’s Name is ultimately destined to denigrate mitzvos, and transgress even the most critical sins.
This became apparent when many Jews unknowingly worshipped Pe’or. The Pe’or service consisted of performing one’s bodily functions in the presence of the idol. This abominable service symbolized the pagan philosophy of satisfying one’s animalistic desires. One had no reason to feel inhibited by anything. The Jews who performed the rite thought they were denigrating the god, while in reality they were actually serving it. By trying to supplement where they should not, they ended up transgressing.
Others, such as Zimri, felt that by relaxing the laws against intimacy with a gentile, Bnei Yisrael would not sin and worship the idol. Horav Yosef Chaim Zonnenfeld, z.l., contends that Zimri came to the defense of the men who were gravitating towards the women outside of the Jewish camp, who, in turn, coerced them to serve the idol. If these women would have been permitted to enter the Jewish camp, Zimri felt the men would not fall prey to idol worship. Once again, an attempt at amending the Divine authority of the Torah resulted in national catastrophe.
We must always remember that there can never be any arbitrary alteration or subjective addition to, or subtraction from the Torah. Tampering with the Word of Hashem by bringing human opinion into the sphere of the Eternal is to blaspheme the integrity of the Torah and reduce it to the level of human superficiality. Such an attempt has ultimately achieved nothing but disaster.