restart the wheels of commerce

restart the wheels of commerce

In early 2009, an article in the New York Times observed: “Without a cure for the problem of bad assets, the credit crisis that is dragging down the economy will linger, as banks cannot resume the ample lending needed to restart the wheels of commerce.” What did the article mean by banks having a problem with “bad assets”? Why is “ample lending” by banks necessary to “restart the wheels of commerce”?
restart the wheels of commerce