It makes sense
Joshua 8: There wasn’t a word of all that Moses commanded that Joshua didn’t read to the entire congregation.
There’s both good news and bad news. The good news is that the Israelites have just won their second major victory. The bad news is that because of Achan’s sin, that victory was preceded by their first defeat. In spite of the clear statement of the Law Achan’s greed led to the deaths of several. Now, Achan, and those close to him, have paid for his sin with his own lives and the humiliation dealt the army of Israel has been erased by the total destruction of Ai. Joshua wisely calls for a time out. The people gather at the twin Mounts of Ebal and Gerisim and Joshua has half the people turn their backs on one of the mountains and the other half turn their backs on its twin. Then Joshua gives them a refresher course on God’s Law. The blessing of the Law is represented by Gerisim and the curse of the Law is represented by Ebal. Clearly, Joshua wants the people to remember that what they’re doing in Canaan isn’t all about combat and conquest. If they don’t remain firmly connected to the Lord God their future is bleak. Their only hope is to remain on the “blessing” side of things. This isn’t magic. In fact, it’s quite practical. Life works better for those who live in a consistent relationship with God than it does for those who reject him and live by some other standard. I realize that there’s more in play here, but I can’t help but note that the bottom line is based on plain good sense.
Take Away: There’s a way of life that is blessed by the Lord.