Numbers 21:4-9. During the wilderness wanderings, Israel complained against God and Moses; the LORD sent fiery serpents among them, and many died of snakebite. When the people repented, God instructed Moses to fashion a bronze serpent and set it on a pole. "Everyone who is bitten, when he sees it, shall live" (Num 21:8). Looking at the bronze serpent — simply looking — was the divinely-specified means of rescue. The object, later called Nehushtan ("the bronze thing"), was kept by Israel and eventually became an object of idolatrous veneration; King Hezekiah destroyed it in His reforms (2 Kings 18:4).
The bronze serpent is one of the most important OT foreshadowings of the cross, and Jesus Himself made the connection explicit: "As Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, that whoever believes in him may have eternal life" (John 3:14-15). Four layers. (1) The cure made in the shape of the curse. The serpents bit Israel; the cure was a serpent-shaped thing. At the cross, Christ who knew no sin was made sin (2 Corinthians 5:21); He took the shape of our curse to cancel it. Paul: "Christ redeemed us from the curse of the law by becoming a curse for us" (Galatians 3:13). (2) Salvation by looking. The Israelite didn't have to climb the pole, fight the snakes, or earn his healing. He looked. "Look to me, and be saved, all the ends of the earth" (Isaiah 45:22). Saving faith is fundamentally looking to Christ — not manufacturing, not performing, not ascending — simply looking. (3) Spurgeon's conversion. Charles Spurgeon was converted at age 15 reading Isaiah 45:22 — "Look unto me, and be ye saved, all the ends of the earth" — in a snowstorm at a Primitive Methodist chapel. The preacher said "Young man, look!" and Spurgeon looked. (4) Danger of the object becoming the idol. By Hezekiah's time the bronze serpent itself was being burned incense to. Hezekiah called it Nehushtan ("just a bronze thing") and smashed it. Object lessons must not become objects of worship. Christ, not the cross-symbol, receives the devotion.