How can God give purpose to life?

I've often heard it said that if God did not exist, life would be without meaning or purpose. What I want to know is how a god can give inherent meaning to anything. I can understand giving purpose to something in the sense that the inventor of a tool had a specific purpose for it in mind when he made it. But that doesn't explain why (if the tool had consciousness) it should be happy with that purpose. Or am I missing something here?