Why would Joel tell people to 'be ashamed' if they haven't sinned? It's not about feeling guilty, but about a deep, public disappointment that shakes you to your core.
The Hebrew word used here for 'ashamed' doesn't always carry the same moral weight as our English word. It can describe the profound feeling of being let down when your hopes are dashed.
Imagine pouring all your energy, resources, and prayers into a harvest, only to see it completely destroyed. The shame Joel describes is the outward expression of that dashed hope. It's the face you show the world when your reliable source of provision has vanished. It's the confusion and dismay that comes when your careful work yields nothing.
This isn't necessarily about a specific sin, but about the devastating impact of God's judgment on the land and livelihoods of the people. Their labor, their security, their very way of life is gone, leaving them exposed and bewildered.