Why would God send snakes to kill people and direct them how to be healed from those same snakes?

Num 21:4-9 ESV  From Mount Hor they set out by the way to the Red Sea, to go around the land of Edom. And the people became impatient on the way.  5  And the people spoke against God and against Moses, “Why have you brought us up out of Egypt to die in the wilderness? For there is no food and no water, and we loathe this worthless food.”  6  Then the LORD sent fiery serpents among the people, and they bit the people, so that many people of Israel died.  7  And the people came to Moses and said, “We have sinned, for we have spoken against the LORD and against you. Pray to the LORD, that he take away the serpents from us.” So Moses prayed for the people.  8  And the LORD said to Moses, “Make a fiery serpent and set it on a pole, and everyone who is bitten, when he sees it, shall live.”  9  So Moses made a bronze serpent and set it on a pole. And if a serpent bit anyone, he would look at the bronze serpent and live.

The short answer

The Lord sent the snakes in righteous judgment. He sent healing in loving mercy after they repented.

What the passage says

1. The people were impatient and very ungrateful. (Judgment deserved)
2. The ‘Lord sent’ the snakes. (Judgment given)
3. The people repented.
4. Moses interceded.
5. The Lord gave instructions for ‘making a snake’. (Mercy offered)
6. When the people looked at the snake they didn’t die. (Mercy received)

Other ‘snake’ passages

Jer 8:16-17 ESV  “The snorting of their horses is heard from Dan; at the sound of the neighing of their stallions the whole land quakes. They come and devour the land and all that fills it, the city and those who dwell in it.  17  For behold, I am sending among you serpents, adders that cannot be charmed, and they shall bite you,” declares the LORD.

Amo 9:1-4 ESV  I saw the Lord standing beside the altar, and he said: “Strike the capitals until the thresholds shake, and shatter them on the heads of all the people; and those who are left of them I will kill with the sword; not one of them shall flee away; not one of them shall escape.  2  “If they dig into Sheol, from there shall my hand take them; if they climb up to heaven, from there I will bring them down.  3  If they hide themselves on the top of Carmel, from there I will search them out and take them; and if they hide from my sight at the bottom of the sea, there I will command the serpent, and it shall bite them.  4  And if they go into captivity before their enemies, there I will command the sword, and it shall kill them; and I will fix my eyes upon them for evil and not for good.”

God’s justice and mercy together

Deu 28:63 ESV  And as the LORD took delight in doing you good and multiplying you, so the LORD will take delight in bringing ruin upon you and destroying you. And you shall be plucked off the land that you are entering to take possession of it.

Deu 30:1-3 ESV  “And when all these things come upon you, the blessing and the curse, which I have set before you, and you call them to mind among all the nations where the LORD your God has driven you,  2  and return to the LORD your God, you and your children, and obey his voice in all that I command you today, with all your heart and with all your soul,  3  then the LORD your God will restore your fortunes and have mercy on you, and he will gather you again from all the peoples where the LORD your God has scattered you.

Deu 32:39 ESV  “‘See now that I, even I, am he, and there is no god beside me; … I wound and I heal; and there is none that can deliver out of my hand.

Rom 11:22 ESV  Note then the kindness and the severity of God: severity toward those who have fallen, but God’s kindness to you, provided you continue in his kindness. Otherwise you too will be cut off.

Heb 10:28,30-31 ESV  Anyone who has set aside the law of Moses dies without mercy on the evidence of two or three witnesses. … For we know him who said, “Vengeance is mine; I will repay.” And again, “The Lord will judge his people.”  31  It is a fearful thing to fall into the hands of the living God.

Conclusion

1. The Lord is a loving Father and a Holy Judge. He is a merciful Deliverer of those who fear Him and He takes vengeance on those who despise Him.
2. The ‘Lord takes delight in doing you good’ and ‘the LORD will take delight in bringing ruin upon you’. (De 28:63)
3. The Lord ‘scatters you to all the nations’ and He ‘restores you and has mercy on you’ (De 20:1-3)
4. The Lord ‘wounds and heals’ (De 32:39)
5. The Lord is ‘kind’ and ‘severe’ (Rom 11:22)