A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
exo 10:1PLAGUE OF LOCUSTS. (Exo. 10:1-20)
show these my signs, &c.--Sinners even of the worst description are to be admonished even though there may be little hope of amendment, and hence those striking miracles that carried so clear and conclusive demonstration of the being and character of the true God were performed in lengthened series before Pharaoh to leave him without excuse when judgment should be finally executed.
exo 10:2And that thou mayest tell . . . of thy son, and of thy son's son, &c.--There was a further and higher reason for the infliction of those awful judgments, namely, that the knowledge of them there, and the permanent record of them still, might furnish a salutary and impressive lesson to the Church down to the latest ages. Worldly historians might have described them as extraordinary occurrences that marked this era of Moses in ancient Egypt. But we are taught to trace them to their cause: the judgments of divine wrath on a grossly idolatrous king and nation.
exo 10:4to-morrow will I bring the locusts--Moses was commissioned to renew the request, so often made and denied, with an assurance that an unfavorable answer would be followed on the morrow by an invasion of locusts. This species of insect resembles a large, spotted, red and black, double-winged grasshopper, about three inches or less in length, with the two hind legs working like hinged springs of immense strength and elasticity. Perhaps no more terrible scourge was ever brought on a land than those voracious insects, which fly in such countless numbers as to darken the land which they infest; and on whatever place they alight, they convert it into a waste and barren desert, stripping the ground of its verdure, the trees of their leaves and bark, and producing in a few hours a degree of desolation which it requires the lapse of years to repair.
exo 10:7Pharaoh's servants said--Many of his courtiers must have suffered serious losses from the late visitations, and the prospect of such a calamity as that which was threatened and the magnitude of which former experience enabled them to realize, led them to make a strong remonstrance with the king. Finding himself not seconded by his counsellors in his continued resistance, he recalled Moses and Aaron, and having expressed his consent to their departure, inquired who were to go. The prompt and decisive reply, "all," neither man nor beast shall remain, raised a storm of indignant fury in the breast of the proud king. He would permit the grown-up men to go away; but no other terms would be listened to.
exo 10:11they were driven out from Pharaoh's presence--In the East, when a person of authority and rank feels annoyed by a petition which he is unwilling to grant, he makes a signal to his attendants, who rush forward and, seizing the obnoxious suppliant by the neck, drag him out of the chamber with violent haste. Of such a character was the impassioned scene in the court of Egypt when the king had wrought himself into such a fit of uncontrollable fury as to treat ignominiously the two venerable representatives of the Hebrew people.
exo 10:13the Lord brought an east wind--The rod of Moses was again raised, and the locusts came. They are natives of the desert and are only brought by an east wind into Egypt, where they sometimes come in sun-obscuring clouds, destroying in a few days every green blade in the track they traverse. Man, with all his contrivances, can do nothing to protect himself from the overwhelming invasion. Egypt has often suffered from locusts. But the plague that followed the wave of the miraculous rod was altogether unexampled. Pharaoh, fearing irretrievable ruin to his country, sent in haste for Moses, and confessing his sin, implored the intercession of Moses, who entreated the Lord, and a "mighty strong west wind took away the locusts."
exo 10:21PLAGUE OF DARKNESS. (Exo 10:21-29)
Stretch out thine hand toward heaven, that there may be darkness--Whatever secondary means were employed in producing it, whether thick clammy fogs and vapors, according to some; a sandstorm, or the chamsin, according to others; it was such that it could be almost perceived by the organs of touch, and so protracted as to continue for three days, which the chamsin does [HENGSTENBERG]. The appalling character of this calamity consisted in this, that the sun was an object of Egyptian idolatry; that the pure and serene sky of that country was never marred by the appearance of a cloud. And here, too, the Lord made a marked difference between Goshen and the rest of Egypt.
exo 10:24Pharaoh called unto Moses, and said, Go ye, serve the Lord--Terrified by the preternatural darkness, the stubborn king relents, and proposes another compromise--the flocks and herds to be left as hostages for their return. But the crisis is approaching, and Moses insists on every iota of his demand. The cattle would be needed for sacrifice--how many or how few could not be known till their arrival at the scene of religious observance. But the emancipation of Israel from Egyptian bondage was to be complete.
exo 10:28Pharaoh said, . . . Get thee from me--The calm firmness of Moses provoked the tyrant. Frantic with disappointment and rage, with offended and desperate malice, he ordered him from his presence and forbade him ever to return.
exo 10:29Moses said, Thou hast spoken well.