That's what happens when you mix your personal beliefs up with business. Most people like eating on Sundays. In addition, many people like working on Sundays (and need the hours/money to better support their families). So... who benefits?
Don't want to work on Sunday because it goes against your beliefs? Perfectly fine... but let those people who don't share your beliefs work (and eat, should they want food from your restaurant).
Interesting that you don't hear about businesses closing on Friday or Saturday though... HMMMMMM... wonder why that could be?