Ray Dalio has a really cool book about this. I'm just starting it myself but I think it would help explain a lot of the questions in this thread. He has a FREE pdf which you can download to any eReader, or you can buy the hardcopy.

You can find it here: https://www.principles.com/big-debt-crises/

The short of it is interest rates are a tool used by the Fed to attempt to control the rate at which people and institutions take on debt. Too much debt = recession. Too little debt = recession. I'm greatly oversimplifying here but Ray does a fantastic job explaining things. If anyone wants to dig in deep I highly, highly recommend you read this book.