To require your customers to have a login to view your categories and products.

If eShop enabled in eShop settings check box Login is required to view listings to set active

If eShop is not enabled this is still possible in the Listings Setup Page check box Login is required to view listings to set active

If your site is set to require customers to login to view your categories and products the rest of the site will still remain visible.

If using the option Limit categories to Customer this option to require users to login will be automatically applied.