Komentarz do Powtórzonego Prawa 28:27

בשחין מצרים [THE LORD WILL SMITH THEE] WITH THE BOILS OF EGYPT — This was very bad, being wet inside and dry on the surface, as is stated in Treatise Bechorot 41a.

בגרב ובחרס, “with wet boils and itch, etc.” The word גרב refers to an itch which the afflicted person scratches with a shard of earthenware. This is the approach taken by most commentators (Ibn Ezra quoting unnamed sources). It is, however, possible to understand the word ובחרס as related to שמש pronounced shamash (Pessikta Zutrata), that this affliction is due to G’d wanting to frighten the victim who faces such an affliction. The affliction is known by three names, שמש, חמה, חרס. The reason it is known as שמש is because man is supposed to be a servant serving his master, which the Jew afflicted with this disease has not been. Seeing that the servant (Israel) is of an especially high-ranking nature, this reflects on his Master and His High Rank. The name חמה reflects the fact that the skin affected becomes especially hot; it is also called חרס, reflecting the fact that the sun is supposed to spread light on earth (Job 9,7). [Both man and the sun have a similar task, the former to provide spiritual enlightenment, the latter to provide physical light. Ed.]
Furthermore, if you examine the three words שמש, חרס, חמה, you will observe that the combined final letters of these three words spell שס'ה (365) an allusion to the number of days in the solar year. This is a reference to the orbit of the sun created on the fourth day of creation. It is the outermost orbit of the four respective orbits, i.e. daily rotation of earth on its axis, the cycle of the week, and the cycle of the month, i.e. lunar orbit. The veiled warning in all this is that if one does not obey the rules laid down by G’d the result will be a universe which will eventually self-destruct due to our not having observed the commandments of the Torah which are part of the laws of nature. [I have translated this somewhat freely. Ed.] The author cites various verses from Scripture such as Judges 14,18, in which the word חרס means “sun.” Seeing that in Psalms 121,6 David appears to view the sun as a negative force, i.e. “the sun will not strike (יככה) you by day nor the moon by night,” it appears that the thrust of David’s words is that disease and malfunctions in nature are all due to faulty eating habits (involuntary at times), or to exposure to an inclement climate. All of these things are caused in one way or an other by the motion of the sun.

Extremely pernicious, etc. Otherwise, why does it say “Egyptian boils”? It should have simply said “boils.”

ובטחורים, and incurable hemorrhoids. Seeing that these ailments originate in hidden regions of the body they cannot be treated medically, and are described in the written text as עפולין, “from a dark place.”

גרב is a wet boil,

Boils that are dry, like ceramics. This is its meaning, because it is [also] written “with dry boils,” thus this indicates that גרב means running boils. See above in parshas Emor (Vayikra 21:20).

Since these ailments have been inflicted by G-d and are not phenomena known in nature, it is evident that physicians cannot deal with this.

חרס is a boil dry as a potsherd (חרס identical with חרש, a potsherd cf. Rashi on Leviticus 21:20).