Musar על פסחים 220:10

There follows פרשת קדושים which deals with how to sanctify oneself, how to get rid of the residual pollutant of the serpent. The very purpose of the legislation in this פרשה is alluded to in 19,26: לא תנחשו, "do not indulge in practices reminiscent of the נחש, the serpent." The Rekanati comments on this verse as follows: "Do not commit the error of following the path of the original serpent which is known as the spirit of impurity, whose actions are known as ניחוש. We know about this from Bileam of whom the Torah reports in Numbers 24,1 that he discontinued consulting נחשים as had been his practice. Such consultations involved calling upon the assistance of impure spirits by swearing some kind of allegiance to them. These spirits are presumed not only to know the future but also to be able to reveal it to man. Anyone who prefers to rely on these spirits will find that G–d withdraws from him, and delivers him up to the mercy of those spirits. This is the meaning of Pessachim 110: כל דקפיד קפדינן בהדיה, "The more one is worried [about the influence of negative forces, מזיקים, Ed.] the more power these forces will have over such a person. When such a person dies, the aforementioned forces will accompany his body in accordance with the statement of our sages: בדרך שאדם רוצה לילך בה מוליכין אותו, "One leads man along the path he has chosen for himself" (Makkot 10). There are other commentators who see a warning in the verse exhorting us not to be מנחש, not to do something similar to what the serpent did when it upset the equilibrium of the Celestial equivalent of Eve by seducing Eve on earth.