Companies spend a lot of time, energy and money answering this for themselves. They hire consultants, develop mantras and mission statements. It's the latest thing in a meaningful, self-reflecting, find your true north sort of exercise. They used to call it branding.
A more important question and answer might be...what are you going to do about it when you find our you're not doing it?...whatever the it was when you defined it in the beginning. Let's say for example you set out to "make people happy" because the "make a profit" answer sounded too shallow and self-serving. Question is...what are you going to do when people (both your employees and customers) tell you they aren't "happy"? Are you prepared to stop or change course...180 degrees if necessary? Would you do whatever it took to get realigned with your core values? While codifying your "why" is important, I think it's equally important to understand the likelihood that you will need to change or scrap the idea altogether. Otherwise, it's just some fancy words in a handbook...perhaps a big lie.
Actions always speak louder than words.