Unbroken seriousness of a melodramatic or somber kind will inevitably communicate a sickness of soul to the great mass of people. This is partly because life as God created it is not like that.
There are, for example, little babies in the world who are not the least impressed with or in need of our passion and zeal and earnest looks. They are cooing and smiling and calling for their daddies to get down and play with them. The daddy who cannot do this will not understand the true seriousness of sin, because he is not capable of enjoying what God has preserved from its ravages. He is really a sick man and unfit to lead others to health. He is, in the end, earnest about being earnest, not earnest about being joyful.
The real battle in life is to be as happy in God as we can be, and that takes a very special kind of earnestness, since God threatens terrible things if we will not be happy.
(HT: Justin Taylor)