At the outset of his presidency, to deal with the banking crisis, roosevelt:

Roosevelt announced a bank holiday and thus closed the banks.

When the Great Depression hit, the people lost their confidence in banks and thus massively went and withdrew their money. This was bad for the economy as whole. Thus in order to restore the economy and restore the confidence in the banks Roosevelt issued a four day bank holiday so he could get Federal Reserve Banks to issue more currency so the banks could meet legitimate demands.