The Lord is merciful. Notice verse 18, “Then the LORD became jealous for his land and had pity on his people.” To the people of Israel, the land was the promise, dating all the way back to Abraham, fulfilled in part with the conquest of Joshua when the people entered into that land “flowing with milk and honey.” The plague of locust and destruction to the land and crops point to a judgment from God, as does the “northerner” in verse 20 (maybe an foreign army?) that is threatening to overtake the land. In an agrarian culture, the land is everything.
So as part of His mercy, the Lord promises to restore the productivity of the land so they would be satisfied. Not only that, there would be abundance. Through this time of difficulty, God pulled the people back to Himself, reminding them that He gave them the land, He sends the rains, He causes the crops to grow. He is the one they should put their trust in.
In the same way God uses difficult examples to pull us back to Him, to remind us of His provision, His love, and His gifts that He gives to us every day.