The problem was that God had declared His all the loot of the siege of Jericho. It was like an offering to God. After that first siege, all subsequent spoils would be free pickings for the Israelite warriors.
Achan couldn’t wait. He scooped up some silver and a fine Babylonian tunic and buried it in his tent. He knew he wasn’t supposed to do that, but, as they say, he couldn’t resist.
As a result of his greed, 36 Israelites were killed in the next attack. God was no longer with them. This sin first had to be purged (and Achan killed), and then the conquest of Canaan could continue unabated.
A little bit of greed got him into big trouble.
Be careful with the endless lust for more and more and more stuff.
While the rest of the world lives on $1-$2 a day, we Westerners have an insatiable appetite for more and more. Such excess is sin. Be content with what you have! 😀