SUPER simplified: When the economy is good, everyone wants to borrow $ for big ticket items - cars, homes - & banks can't handle everyone borrowing at once, esp at such low interest rates. Bubbles get created, like the housing market recently, where everyone wants a house & sellers jack up their prices. These bubbles eventually pop, which leaves huge #s of people upside-down on those loans, which leads to mass foreclosures/repossessions, which can trigger recession/depression.
@FireMonkey
Raising interest rates can control over-borrowing/irresponsible lending, which can help prevent bubbles that ruin the economy and people's lives. In a perfect world, the balance is between interest rates being not too high that people can't borrow, but not so low we get a bubble. It's about stability.