Earnestness is the demeanor that corresponds to the weight of the subject matter of preaching — and life. The opposite of earnest is not joyful, but trivial, flippant, frivolous, chipper.
It is possible to be earnest and have elements of humor, though not levity. Spurgeon had a way with words, for example, that caused some foolish things to look ludicrous. “Live on the substantial doctrines of grace, and you will outlive and out-work those who delight in the pastry and syllabubs of ‘modern thought.’” (Lectures to My Students, 310).
Now “syllabubs” is an extraordinary word! I don’t know how many of his people knew it. It means “a sweetened drink or topping made of milk or cream beaten with wine or liquor and sometimes further thickened with gelatin and served as a dessert.” It is a funny-sounding word. But he probably did not smile and there was no calculated pause for the laughter to register. He is earnest, but not so solemn in his earnestness that he cannot experience human folly as both sad and comical.
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.