Question: "Why did God judge the sin of Achan so severely?"
Answer: The story of Achan’s sin and God’s punishment is found in Joshua 7. Achan was an Israelite who fought the battle of Jericho with Joshua. God had commanded the Israelites to destroy the entire city of Jericho because of its great sin. Only Rahab the harlot and her household were spared because she had hidden the Israelite spies (Joshua 6:17). God further commanded that, unlike most victories when soldiers were allowed to take the spoils, the Israelites were to take nothing from Jericho. Everything in it was “accursed” or “devoted to destruction.” God warned that anyone taking spoils from Jericho would “make the camp of Israel liable to destruction and bring trouble on it” (Joshua 6:18-19). The Israelites obeyed, except for Achan, who stole a beautiful robe and some gold and silver and hid these things in his tent.
His sin was discovered, of course (Numbers 32:23). God commanded that Achan and his entire family and all his possessions be destroyed, a punishment that seems overly harsh to us today. How are we to understand this dire act of God? There are several reasons for the severe penalty God inflicted upon Achan. For one thing, Achan’s sin affected the entire nation of Israel. In Joshua 7:1 God says that “the Israelites” acted unfaithfully and that His anger burned “against Israel.” The nation as a whole was in a covenant relationship with God and, when one member transgressed that covenant, the entire nation’s relationship with Him was damaged. Achan's sin defiled the other members of the community as well as himself. A similar situation is seen in the sin of Adam and Eve and its effect on the whole of mankind. Adam and Eve’s rebellion destroyed the perfect communion the human race would have enjoyed with God.
Further, Achan’s sin caused God’s blessing upon the Israelites to be withheld in their subsequent battle against the city of Ai, and the Israelites “were routed by the men of Ai, who killed about thirty-six of them” (Joshua 7:4-5). Thirty-six innocent men died because of Achan’s sin. He stole that which was “devoted to destruction” and so brought destruction on others. God explained to Joshua, “That is why the Israelites cannot stand against their enemies; they turn their backs and run because they have been made liable to destruction” (Joshua 7:12; see also 22:20). We fool ourselves if we think that our sin affects only us. Disobedience brings ruin even upon the innocent. Sin’s effects go beyond the initial sinner.
Also, the gold and silver Achan stole was stolen from God Himself. The precious metals were to be added to the treasury of the Lord, and, in stealing them, Achan robbed God directly. Achan’s disobedience was also an insult to God’s holiness and His right to command His people in the manner He sees fit. Even so, God gave Achan a night to consider his sin and come to Him in repentance (Joshua 7:13). Achan did not avail himself of God’s mercy and patience, however. The gold and silver Achan coveted had a stronger pull on his allegiance. Is it any wonder that, in the face of such insult, God would choose to destroy him?
But why, we might ask, did God destroy Achan’s family as well? The Bible doesn’t give us God’s exact reasons for destroying Achan’s family, although Proverbs 15:27 does say that “a greedy man brings trouble to his family.” In the case of Achan, all we can do is speculate. Perhaps it was an object lesson to the rest of the nation, a lesson they learned after Korah’s rebellion (Numbers 16) but which needed to be reinforced. Perhaps Achan’s children had already begun to exhibit their father’s traits of covetousness, disobedience, and disrespect for God’s commands. Most likely, they had actually helped Achan hide the stuff and were, in fact, accomplices to the crime.
There is no way to know all of God’s reasons for what seems to us His harsh punishment of Achan and his family. He doesn’t always explain His reasoning to us, nor does He have to. The story of Achan and many other biblical narratives give us sufficient information to understand that God is holy and that He is not to be disobeyed without risking dire consequences.