God is in a smiting mood, what else is new? This time he's going to rain down environmental destruction on the Israelites, first with worms that will eat all the fruit, then with something that will kill all the vines and trees, thus rendering all the offerings impossible to offer and making the animals desperately unhappy. Then he'll set fire to everything.
The day of the lord is coming! And it's going to be dark and gloomy, because for all the bible occasionally pays lip service to rewarding the faithful, it's much more fun to talk about how the sinners will be punished.
First, god will send a fleet of fiery chariots with warriors who cannot be killed, even if you stab them with a sword. Then the sky will turn pitch black and god will tell the people that if they just turn their hearts towards him and repent, he'll forgive them and give them corn again.
A few warning signs that the day of the lord is nigh: Wonders in the heavens and in the earth, blood, and fire, and pillars of smoke. The sun shall be turned into darkness, and the moon into blood. (v. 30-31)
Okay, so what else happens before the day of the lord? Well, people will be scattered, mostly for selling their kids in exchange for alcohol. That's probably for the best. Then he'll free all the Israelites that the Tyreans and Zidonians have sold to the Greeks so the Israelites can sell their former slave-owners to the Sabeans. Somehow, that doesn't make it right.
Back in Isaiah, we were promised that we could beat our swords into ploughshares because there would be everlasting peace. Now Joel instructs us to Beat your plowshares into swords and your pruninghooks into spears (v. 10).
Then he repeats the rigamarole about the sky going dark and earthquakes, but adds something new: the banishment of foreigners from Jerusalem. Good luck with that one.