When one studies the pasukim (21:4-9) with the miforshim, we find that several aveiros were committed at this time, which resulted in biting snakes. Bnei Yisroel were about to enter Eretz Yisrael. They asked Edom for permission to pass through his land, but Edom refused. They had to travel around the outskirts of his land to find another route into Eretz Yisrael, and that is when the nation panicked. Rashi (21:4) writes, "They said, 'We are so close to entering the Land, and now we are turning back. So did our fathers turn back and remained in the desert for thirty-eight years, until today.' They became disheartened by the hardship of traveling."
ובמשה באלקים העם וידבר, the nation complained against Hashem and against Moshe, and they complained about the manna, which was their only source of food. They were punished with snakes. Rashi (21:6) explains, "Let the snake, which was punished for speaking slander, come and punish those who spread slander. Let the snake, for which all types of food taste the same, come and punish those ingrates (kafuy tovah), for whom one thing [the manna] changes into various tastes." Baal HaTurim writes that they were punished "because they acted like a snake, to speak lashon hara on the manna." The Or HaChaim writes, "It is because Bnei Yisrael spoke lashon hara against Moshe, and then they spoke lashon hara even against Hashem." It states (21:5) ובמשה באלקים העם וידבר, "The nation spoke against Hashem and Moshe..." Rashi writes, לקונו עבד השוו, "They equated the servant with his Master."
Because of these aveiros, they were punished with snakes, and many people died. The nation repented and asked Moshe to daven for them. Hashem gave them a cure, as it states (21:8) נס על אתו ושים שרף לך עשה וחי אתו וראה הנשוך כל והיה, "Make yourself a serpent and put it on a pole, and let whoever is bitten look at it and live." The Mishnah (Rosh Hashanah 29.) asks, "Does a snake cause death or life? Rather, when the Jewish nation looked heavenward and subjected their hearts to their Father in heaven, they were healed, but if not, they would waste away." In other words, their cure came from turning to Hashem.
The Sfas Emes (Chukas ו"תרל) asks, why did there need to be a copper snake in the first place? Why didn’t Hashem simply command the nation to look up at the sky to be healed?
The Sfas Emes replies, "The [copper] snake had the segulah of refuah. Hakadosh Baruch Hu gave it that segulah, as the Ramban writes that it is Hakadosh Baruch Hu's way to sweeten bitterness with bitterness. Therefore, according to nature, for someone bitten by a wild dog, seeing a dog will harm him more; Hakadosh Baruch Hu did the opposite here, that they were cured by looking at the snake. Nevertheless, Hashem's will is that even when we do acts of refuah according to nature, one should look up to heaven. His heart should be to heaven. He should think, 'Could this [copper] snake cure and give life?' This is the meaning of Chazal, לבם ומשעבדין מסתכלין; they should devote their hearts to heaven. Even while engaged in natural healing, their eyes should focus on heaven. This is the meaning of עשה שרף לך, which means that a person's hislahavus should be to connect with Hashem."
Hashem wanted them to be occupied with refuos while simultaneously turning their hearts to Hashem, the true source of refuah. The same occurs today when someone takes medicine and is occupied with refuos. Although he is taking worldly steps toward refuah, his heart should be to Hashem, the source of refuah.
The Ramban (21:9) writes, "It is the way of the Torah that all of its ways are נס בתוך נס, one miracle within another miracle. Hashem removes the illness with the matter that caused the damage... As Chazal say (Mechilta, Shemos 15:25) עץ 'ה ויורהו (that the bitter waters in Marah were healed when a bitter branch was thrown into the waters), and it states (Malachim 2, 2:21) regarding the salt with Elisha (that the waters of Yericho were salty and bitter, and Elisha cured the waters when he poured salt into the origin of the water. For this is Hashem's way, to heal bitterness with bitterness)."
"It is known from the paths of medicine that those bitten by a poisonous animal will be in greater danger when they see the species that bit them or when they see a resemblance of the species that bit them... Doctors are cautious not to even mention the species before them because if the patient thinks about the animal that bit them, it can kill them. Therefore, it would seem proper that those bitten by poisonous snakes should not look at snakes or think about snakes at all.
"Hakadosh Baruch Hu commanded Moshe to make a form of a snake, which caused the death. Just mentioning a snake should cause danger, but HaKadosh Baruch Hu wanted to cure them with something that naturally should cause the opposite. When they looked at the snake, they would be healed. And this was to teach them that Hashem causes death and life." It was a נס נס בתוך, a double miracle because they were healed by something that should have made them even more ill.
Medications are generally bitter and often have negative side effects. How could something bitter and harmful cure? This is how Hashem made refuos, that bitterness will cure bitterness, so we should know that the refuah is from Hashem.
