Financial markets are institutions and procedures that facilitate transactions in all types of financial claims. Financial markets perform the function of allocating savings in the economy to the ultimate demander(s) of the savings. Without these financial markets, the total wealth of the economy would be lessened. Financial markets aid the rate of capital formation in the economy.
The economy would be worse of without financial markets for several reasons. Savers would not be able to earn a return on their savings. People who need capital wouldn't be able to get the funds from other people and so would have to rely only on their own money. The inability to get capital from others would slow the growth of businesses and reduce the purchases of consumers because they can no longer get loans. These would lead to decreased demand for products and services as well as a decrease in available jobs both of which would harm the economy