פירוש על מלכים ב 18:4

And he called it Nechushton. A derogatory expression,³The additional “nun” to the word נחשת serves to belittle and mock the subject. See II Shmuel 13:20. as though to say, “Why is this necessary?⁴The copper serpent was not destroyed before now because it was incorrectly believed that one may not destroy any object that was made as a result of a Divine command. The serpent was originally made to encourage the Bnei Yisroel to pray to God after they were bitten by poisonous snakes. See Bamidbar 21:4-10 and Tosfos in Maseches Chulin 7a. It is also possible that they kept the copper serpent as a remembrance of the great miracle that occurred, just as they kept the jar of manna, in Shemos 16:33-35. It is nothing but a copper serpent.”⁵Alternatively, the Bnei Yisroel who were worshiping it called it the Nechushton.—Targum