What makes people cheerful? God makes them cheerful at the cheerful times. When they doubt God, then they become cheerless. If they trust God, they can be cheerful in many troubles. God makes them cheerful.
People are cheerful comfortable conditions of life and lack of health problems, and not faith in God. Many atheists are much happier than religious people. It seems to me that sometimes religious people are unable to enjoy life because of the stupid prohibitions of their religion.
The big difference is that if the person is a Christian, his happiness goes on into eternity, while the atheist's happiness ends at death if not sooner.