Numbers 21:6 - Joseph Benson’s Commentary on the Old and New Testaments

Fiery serpents Hebrew, נחשׁים, nechashim, the plural of the word translated serpent, Genesis 3:1, where Moses speaks of the temptation and fall of our first parents, and which, when intended of a living creature, we believe, always means a serpent of one species or other, and is accordingly uniformly so rendered, not only by our translators, in the Scriptures, but by the Seventy, and in most or all other versions whatever; and, what certainly ought to have great weight with Christians, by the evangelists and apostles, whenever they quote or refer to those passages of the Old Testament where the word occurs: see on Genesis 3:1. There were many such serpents as Moses here speaks of in this wilderness, which, having been hitherto restrained by God, were now let loose and sent among them: see Jeremiah 8:17. They are called fiery from their effects, because their poison caused an intolerable heat, burning, and thirst, which was aggravated with this circumstance of the place, that there was no water, Numbers 21:5.