The Bible says that being merry (cheerful) is like having the choicest food every day of your life. Yes, the merry heart is a feasting heart. Mish-teh, the Hebrew word for feast, used here, is a symbol of gastronomic banqueting pleasure.
Alternatively, the Bible says that a cheerful heart has medicinal properties, for it protects the mind and the body from ailments that are a result of stress. Therefore being happy is adding to our overall well-being.
Pro_17:22 A merry heart doeth good like a medicine: but a broken spirit drieth the bones
Conversely, being sad can crush, crush us of everything that the French say is: joie de vivre (a feeling of great happiness and enjoyment of life). And sadness, by the way, is the emotional attitude of the ungrateful person. For he always looks at people better, and compares himself with them; for he never counts his blessing, never looks at people lesser, poorer and worse. And true to the saying, he shrinks: mentally, emotionally and spiritually.
Also, being happy is a commandment, for Jesus said: take no thought for your life (where? You find it for yourself). Taking thought, that is worrying, is in violation to Jesus’ commandment. Worrying is sinning. Worrying is questioning the ability of Him who had said: that if He can take care of the birds in the air how much better could he take care of us. Worrying is disobeying Him who had said: take no thought, saying , what shall we eat? or, What shall we drink?…which of you by taking thought (worrying) can add to anything productively.
Thankfulness is at the heart of human well-being; and thanklessness at the heart of human misery.