Rashi notes that the signs of a burn and the signs of a boil are the same, yet the Torah treats them separately in order to indicate that their effect are not to be added to one another. In the event that a mark half the size of a bean of a boil and half the size of a bean of burning appears on the skin, they are not judged as a whole bean. Horav Moshe Feinstein Z”l suggests that a spiritual message may be derived from this halacha, but we must first understand another statement regarding these two plagues. The Torah elsewhere states that one is defiled by a boil if a white rising or reddish-white spot appears in its place. Regarding a burn, on the other hand, the Torah describes it turning in to a reddish-white bright spot or a white bright spot. This seems peculiar, for the same laws apply if the boil turns into a white bright spot or if the burn turns into a white rising! Indeed, these plagues are not mere physical occurrences, but rather Hashem’s way of miraculously alerting an individual to his spiritual afflictions, so that he can repent for his sins. Obviously, the severity of the plague is consistent with the negative character of the transgression. Consequently, one will carefully consider the quality and extent of the physical pain, reflect upon his actions, and offer the proper penance for his actions.
A boil is the result of a wound, while a burn is the result of a fire. The latter naturally evokes a greater reaction, since its source is more frightening. One whose transgression was of a lesser degree would first be afflicted with boils. If this does not serve as a stimulus to repentance, the boil then becomes a white rising or a reddish-white bright spot. One whose sin reflects a greater miscreancy would be beset with a burn, which upon his refusal to recognize its source would turn into a bright spot, white like snow or a reddish-white spot. The sources of these two physical afflictions are distinct, and, therefore their measurements cannot be combined. The nature of the sin determines the extent of the punishment. Various situations will evoke different responses. Although we do not have these plagues today, we must be cognizant that we should interpret every pain which we feel as Hashem’s signal to us. Nothing happens in this world which is not preordained by Hashem. This is a sign of Hashem’s beneficence to us, in the way a loving father admonishes his child before he strays too far on dangerous path.