Proverbs 15:13
A merry heart maketh a cheerful countenance.
A person who is happy on the inside cannot help but show it. Conversely, a grouch has a miserable look on his or her face. A little song that the children sometimes sing says: “If you’re happy and you know it, clap your hands.” A happy Christian will indeed know it and it will be evident - by a contented, happy face.