Observe here, concerning the plague of boils and blains,
I. When they were not wrought upon by the death of their cattle, God sent a plague that seized their own bodies, and touched them to the quick. If less judgments do not do their work, God will send greater. Let us therefore humble ourselves under the mighty hand of God, and go forth to meet him in the way of his judgments, that his anger may be turned away from us.
II. The signal by which this plague was summoned was the sprinkling of warm ashes from the furnace, towards heaven (Exo 9:8, Exo 9:10), which was to signify the heating of the air with such an infection as should produce in the bodies of the Egyptians sore boils, which would be both noisome and painful. Immediately upon the scattering of the ashes, a scalding dew came down out of the air, which blistered wherever it fell. Note, Sometimes God shows men their sin in their punishment; they had oppressed Israel in the furnaces, and now the ashes of the furnace are made as much a terror to them as ever their task-masters had been to the Israelites.
III. The plague itself was very grievous - a common eruption would be so, especially to the nice and delicate, but these eruptions were inflammations, like Job's. This is afterwards called the botch of Egypt (Deu 28:27), as if it were some new disease, never heard of before, and known ever after by that name, Note, Sores in the body are to be looked upon as the punishments of sin, and to be hearkened to as calls to repentance.
IV. The magicians themselves were struck with these boils, Exo 9:11. 1. Thus they were punished, (1.) For helping to harden Pharaoh's heart, as Elymas for seeking to ;pervert the right ways of the Lord; God will severely reckon with those that strengthen the hands of the wicked in their wickedness. (2.) For pretending to imitate the former plagues, and making themselves and Pharaoh sport with them. Those that would produce lice shall, against their wills, produce boils. Note, It is ill jesting with God's judgments, and more dangerous than playing with fire. Be you not mockers, lest your bands be made strong. 2. Thus they were shamed in the presence of their admirers. How weak were their enchantments, which could not so much as secure themselves! The devil can give no protection to those that are in confederacy with him. 3. Thus they were driven from the field. Their power was restrained before (Exo 8:18), but they continued to confront Moses, and confirm Pharaoh in his unbelief, till now, at length, they were forced to retreat, and could not stand before Moses, to which the apostle refers (Ti2 3:9) when he says that their folly was made manifest unto all men.
V. Pharaoh continued obstinate, for now the Lord hardened his heart, Exo 9:12. Before, he had hardened his own heart, and resisted the grace of God; and now God justly gave him up to his own heart's lusts, to a reprobate mind, and strong delusions, permitting Satan to blind and harden him, and ordering every thing, henceforward, so as to make him more and more obstinate. Note, Wilful hardness is commonly punished with judicial hardness. If men shut their eyes against the light, it is just with God to close their eyes. Let us dread this as the sorest judgment a man can be under on this side hell.

Handfuls of ashes of the furnace - As one part of the oppression of the Israelites consisted In their labor in the brick-kilns, some have observed a congruity between the crime and the punishment. The furnaces, in the labor of which they oppressed the Hebrews, now yielded the instruments of their punishment; for every particle of those ashes, formed by unjust and oppressive labor, seemed to be a boil or a blain on the tyrannical king and his cruel and hard-hearted people.

And the Lord said unto Moses and unto Aaron,.... This very probably was the day following, on the third day of the month Abib, about the eighteenth of March, that orders were given to bring on the following plague:

take to you handfuls of ashes of the furnace; either in which the bricks were burnt, or rather in which food was boiled, since it can scarcely he thought there should be brickkiln furnaces so near Pharaoh's court; though perhaps some reference may be had to them, and to the labour of the children Israel at them, and as a just retaliation for their oppression of them in that way. These ashes were such as were blown off the coals, and though fresh, yet not so hot but that they could take and hold them in their hands:

and let Moses sprinkle it towards the heaven, in the sight of Pharaoh; this was to be done before Pharaoh, that he might be an eyewitness of the miracle, he himself seeing with his own eyes that nothing else were cast up into the air but a few light ashes; and this was to be done towards heaven, to show that the plague or judgment came down from heaven, from the God of heaven, whose wrath was now revealed from thence; and Moses he was to do this; he alone, as Philo (z) thinks, or rather both he and Aaron, since they were both spoken to, and both filled their hands with ashes; it is most likely that both cast them up into the air, though Moses, being the principal person, is only mentioned.

(z) De Vita Mosis, l. 1. p. 622.

PLAGUE OF BOILS. (Exo 9:8-17)

Take to you handfuls of ashes, &c.--The next plague assailed the persons of the Egyptians, and it appeared in the form of ulcerous eruptions upon the skin and flesh (Lev 13:20; Kg2 20:7; Job 2:7). That this epidemic did not arise from natural causes was evident from its taking effect from the particular action of Moses done in the sight of Pharaoh. The attitude he assumed was similar to that of Eastern magicians, who, "when they pronounce an imprecation on an individual, a village, or a country, take the ashes of cows' dung (that is, from a common fire) and throw them in the air, saying to the objects of their displeasure, such a sickness or such a curse shall come upon you" [ROBERTS].