And the LORD sent {d} fiery serpents among the people, and they bit the people; and much people of Israel died.

(d) For they that were bitten by them were so inflamed by the poison of them, that they died.

Wesley's Notes

21:6 Fiery serpents - There were many such in this wilderness, which having been hitherto restrained by God, are now let loose and sent among them. They are called fiery from their effects, because their poison caused an intolerable heat and burning and thirst, which was aggravated with this circumstance of the place, that here was no water, Num 21:5.

Jamieson-Fausset-Brown Bible Commentary

6. The Lord sent fiery serpents among the people-That part of the desert where the Israelites now were-near the head of the gulf of Akaba-is greatly infested with venomous reptiles, of various kinds, particularly lizards, which raise themselves in the air and swing themselves from branches; and scorpions, which, being in the habit of lying in long grass, are particularly dangerous to the barelegged, sandaled people of the East. The only known remedy consists in sucking the wound, or, in the case of cattle, in the application of ammonia. The exact species of serpents that caused so great mortality among the Israelites cannot be ascertained. They are said to have been "fiery," an epithet applied to them either from their bright, vivid color, or the violent inflammation their bite occasioned.

Matthew Henry's Concise Commentary

21:4-9 The children of Israel were wearied by a long march round the land of Edom. They speak discontentedly of what God had done for them, and distrustfully of what he would do. What will they be pleased with, whom manna will not please? Let not the contempt which some cast on the word of God, make us value it less. It is the bread of life, substantial bread, and will nourish those who by faith feed upon it, to eternal life, whoever may call it light bread. We see the righteous judgment God brought upon them for murmuring. He sent fiery serpents among them, which bit or stung many to death. It is to be feared that they would not have owned the sin, if they had not felt the smart; but they relent under the rod. And God made a wonderful provision for their relief. The Jews themselves say it was not the sight of the brazen serpent that cured; but in looking up to it, they looked up to God as the Lord that healed them. There was much gospel in this. Our Saviour declared, Joh 3:14,15, that as Moses lifted up the serpent in the wilderness, so the Son of man must be lifted up, that whatsoever believeth in him, should not perish. Compare their disease and ours. Sin bites like a serpent, and stings like an adder. Compare the application of their remedy and ours. They looked and lived, and we, if we believe, shall not perish. It is by faith that we look unto Jesus, Heb 12:2. Whosoever looked, however desperate his case, or feeble his sight, or distant his place, was certainly and perfectly cured. The Lord can relieve us from dangers and distresses, by means which human reason never would have devised. Oh that the venom of the old serpent, inflaming men's passions, and causing them to commit sins which end in their eternal destruction, were as sensibly felt, and the danger as plainly seen, as the Israelites felt pain from the bite of the fiery serpents, and feared the death which followed! Then none would shut their eyes to Christ, or turn from his gospel. Then a crucified Saviour would be so valued, that all things else would be accounted loss for him; then, without delay, and with earnestness and simplicity, all would apply to him in the appointed way, crying, Lord, save us; we perish! Nor would any abuse the freeness of Christ's salvation, while they reckoned the price which it cost him.