In Chapter 22, God shows Jeremiah two baskets of figs placed before God's temple. But it's not lunchtime; it's moral lesson time. Come on—we're talking about God here. He's not feeding you figs without some sort of greater purpose in mind. Making Fig Newtons, maybe?
So here's the greater symbolic purpose: one of the baskets contains really good figs, premium figs, Whole Foods quality stuff. But the other basket has bad figs, which are so bad that they can't be eaten, even in Fig Newton form. God says that the good figs symbolize the people of Judah who will survive the Babylonian exile and eventually return. The bad figs are King Zedekiah, the royal officials, the people who will remain in Judah and Jerusalem, and those who live in Egypt. They'll all endure tremendous suffering and will probably die from war, disease, or famine.
Vegetation imagery pops up a lot in the prophets. People are like fruit that God grows on a vine. If it turns out to be good fruit, God will take it (and probably metaphorically bake it into a pie or make wine out of it or something, though we don't know what that would mean). But if it's bad fruit, he'll squash it and burn down the whole field or vineyard as well. He doesn't do anything halfway.
Grapevines and fig trees are often used in the Bible as symbols of prosperity. The prophet Micah (4:4) described a time of peace when "they shall all sit under their own vines and under their own fig trees, and no one shall make them afraid." Having your own vines and fig trees was kind of like having two cars in the garage and a freezer full of Ben & Jerry's Chunky Monkey.