The Torah tells us that the G-d-fearing Egyptians brought their animals indoors for fear of the hail which would strike the country. Chazal derive from here Tov she’b’nechashim ratzutz es mocho, “The best of snakes, smash his head.” (In other words, there is no such thing as a good snake.) Chazal base this statement on the fact that, when Pharaoh required chariots and horses, he had to obtain these horses from someone. Since all of Egypt’s animals had been killed, from where could Pharaoh have gotten the animals? Apparently, the G-d-fearing Egyptians who had saved their animals by listening to Hashem later contributed to Pharaoh’s war machine. The G-d-fearing Egyptians were far from G-d-fearing – once the danger had passed. Chazal are teaching us that a snake remains a snake. Even if the snake earns the appellation of yarei es dvar Hashem, how is it possible for him to sustain this trait? If he fears G-d, he obviously fears acting like a snake. This is what Chazal are teaching us: a snake is a snake. The finest, most G-d-fearing snake remains a snake. His frumkeit will not prevail over his basic nature.
Horav Baruch Mordechai Ezrachi, Shlita, supplements this with an insightful lesson. As long as the basic nature of the snake (or anyone for that matter) is not expunged, it will remain an inherent dormant part of the subject – even if it is supposedly concealed by yiraas Shomayim! True yiraas Shomayim is not an external quality. It is real; it is intrinsic, being part and parcel of the subject’s character, personality and essence. Unless the person/subject is able to transform his essence completely, such that the yiraas Shomayim extirpates any and every vestige of serpentine tendency from within, he remains a nachash, snake. Therefore, the only antidote to his poison is to smash his head.
Yiraas Shomayim should change the person. It is a transformative quality which is not merely superficial, (example: the person merely puts on frum “airs.”) If he does not intrinsically change, his frumkeit is to no avail. It is not real. Sadly, we may observe individuals who manifest external signs of being devout and G-d-fearing; yet, when “push comes to shove” under pressure, they suddenly resort to acting in a manner totally unbecoming anyone of such a lofty spiritual connection. This is an indication that what you see is all that there is. Covert yiraas Shomayim sadly has no internal influence on the person.
Rav Ezrachi supports this from the fact that the G-d-fearing Egyptians, when confronted with the dilemma of listening to Pharaoh or saving their animals, did what was right and brought their animals inside. They demonstrated (what was supposedly) their yiraas Shomayim, which transcended their fear of Pharaoh and of public opinion, but it was not inherent. It had not transformed their essential natures, for, when Pharaoh needed chariots to chase the fleeing Jews, these G-d-fearing Egyptians were prepared to give him their horses. I guess they were not that G-d-fearing after all. Later on, however, when Pharaoh needed animals, he knew exactly whom to ask. Their yiraas Shomayim was superficial. It had not become part of their psyches.