Jabin was a bad dude. He was the king of a city-state called Hazor in northern Canaan. As the largest city in the region, Jabin was the strongest king in the region, and all the other kings and cities bowed to his will. When Jabin heard about the success that Joshua and the Israelites were having in conquering the southern region of Canaan, he called in his banners and all of the kings of the northern region prepared for war against Israel. "And they came out with all their troops, a great horde, in number like the sand that is on the seashore, with very many horses and chariots." (Joshua 11.4, emphasis mine) God grants Israel the victory, however, and after the battle they controlled the lion's share of Canaan.
But although Israel has enjoyed several military victories there was still more land to be conquered. Sure, Israel had established itself as a military force to be reckoned with, and their strength was only increasing, With a few more tools, they would be unstoppable. This is why, after the battle with Jabin and the northern kings, it would seem only natural that Israel would acquire the spoils of war - the "very many horses and chariots" of their enemies. Surely having horses and chariots would be very helpful in the completion of their conquest of the Promised Land, and would only serve to make them an even more formidable force for their enemies to reckon with.
But this is not what they do. Instead, God gives them an instruction in verse 6: "You shall hamstring (cripple) their horses and burn their chariots with fire." On its face, this command doesn't seem to make any sense at all: why get rid of something so valuable like horses and chariots, especially when there was still more land to conquer and battles to fight? After all, horse-drawn chariots were the pinnacle of military technology at the time, and they would certainly have come in handy as the Israelites continued to sweep through the land. Why, God? Why disable and destroy such valuable tools of warfare? Regardless of these unanswered questions, Joshua does as he's told: "And Joshua did to them just as the Lord said to him: he hamstrung their horses and burned their chariots with fire." (verse 9) Although the command may have been confusing to Israel at the time, as we look back on this story, there are at least two clear reasons why God instructed the Israelites not to use horses and chariots in their military endeavors.
1. To remind Israel that God alone is sovereign over the battle.
If the Israelites had horses and chariots to fight their battles, it could be very easy for them to be tempted to think that their might and victory came from horses and chariots and not from God. And that is not something that God will allow to happen to them. In fact, it seems that God wants his people to engage in their battles from what appears to be a position of weakness so that it will be clear to them - and to their enemies - that the only reason they are successful is because God is fighting for them. And so, in order to drive that point home, God tells them to cripple the horses so they will never pull another chariots, and burn the chariots so they will never again be used in battle. The message is this: God is sovereign over the battle, and victory comes from him. Not from horses; not from chariots; not from strategy; not from strength; not from superior weaponry; not from anything but from God.
Recovering alcoholics will commonly go to great lengths to avoid settings and locations that contain alcohol. This means they stop going to bars and restaurants that serve alcohol, and they might even stop hanging out with friends who drink. Put simply, they know that even being in the presence of alcohol will be a strong temptation to relapse into their old behaviors. This is similar to how God is dealing with the Israelites: he knows that if they have horses and chariots they will be tempted to put their trust in horses and chariots rather than in him. So to keep that from happening, he has them remove the temptation altogether.
2. To show Israel that the best that man has to offer amounts to nothing.
The horse-drawn chariot was the heigh of military technology in Joshua's day. All of the best and strongest armies employed horses and chariots in their conquests, and the army with the most chariots had the decisive advantage on the battlefield. So then, in telling his people to get rid of all the horses and chariots, God is showing them that the best that mankind has to offer to help them in their endeavors amounts to nothing when compared to the sovereign power and action of God fighting on your behalf. Imagine walking onto a modern battlefield where guns, bombs, mortars, and every other type of deadly weapon is aimed right at you, and you've only been given a rubber band to shoot with your thumbs. The power of God is so immense that horses and chariots amount to the tactical advantage of of a rubber band in comparison.
21st century horses and chariots
Unlike Israel, you and I are not engaged in a campaign to claim the Promised Land, and we're not fighting armies and inheriting horses and chariots as the spoils of war. But, like Israel, you and I certainly have things in our lives that can tempt us to take our focus off of trusting in God and his provision and sovereignty in our lives. Imagine the security that having horses and chariots would have brought the Israelites. They probably would have slept better at night knowing they had horses and chariots; they probably would have felt more confident and bold and encouraged if they had horses and chariots. But the security of horses and chariots is nothing compared to the security of trusting the sovereign Lord of the universe. Israel didn't need horses and chariots. They needed God.
We likewise struggle with putting our trust and hope in things rather than God. But the reality is that those things have no power compared to the sovereign rule and reign of the Creator of the universe. Maybe you think if you just get ahead at work and get that promotion and salary increase that things will finally start turning around for you. That's not true. If you think that money will solve your problems, then you're trusting in horses and chariots. You need to burn that chariot, because it's keeping you from realizing that God is sovereign over your life and that your hope is in him, not in your paycheck. Every time you trust in something for your security over and above the sovereign Lord of the universe, you're keeping a hors and chariot for yourself. But God wants you to burn those chariots and hamstring those horses. You don't need those things; you need God.
Psalm 33.17: The war horse is a false hope for salvation, and by its great might it cannot rescue. So is anything in which you put your trust, because the best the world or you can offer amounts to nothing when compared to God's abilities. Your status or wealth or power or good works are false hopes for salvation - by their great might they cannot rescue. Only God rescues.
Psalm 20.7: Some trust in chariots and some in horses, but we trust in the name of the Lord our God.