The bronze serpent Moses is commanded to raise so that anyone bitten by the wilderness snakes could look at it and live (Numbers 21:4-9) has a striking sequel centuries later: the book of Kings records that this same object, by then called Nechushtan, was still preserved and had become an object of incense-burning and worship in its own right, prompting King Hezekiah to destroy it as part of his religious reforms (2 Kings 18:4). A healing sign the Torah presents as a divinely sanctioned, one-time remedy had, by the account of Kings, been kept as a physical relic and turned into an idol, illustrating a recurring biblical concern that even an object associated with a genuine act of divine mercy could become, over generations, a focus of forbidden worship in its own right.
Source critics generally attribute the bronze serpent episode, along with the surrounding wilderness complaint narratives, to older narrative material later incorporated into the Priestly framework that dominates most of Numbers, and note that the episode's underlying imagery, a raised image offering protection from the very kind of harm it depicts, has few close parallels elsewhere in the Torah's own legal or narrative material.