Christians should be grave and serious, though cheerful and pleasant. They should feel that they have great interests at stake, and that the world has too. They are redeemed—not to make sport; purchased with precious blood—for other purposes than to make men laugh. They are soon to be in heaven—and a man who has any impressive sense of that will habitually feel he has much else to do than to make men laugh. The true course of life is midway between moroseness and levity; sourness and lightness; harshness and jesting. Be benevolent, kind, cheerful, bland, courteous—but serious. Be solemn, thoughtful, deeply impressed with the presence of God and with eternal things—but pleasant affable and benignant. Think not a smile sinful; but think not levity and jesting harmless.It's worth giving thought to this. I guess most of us will incline to extreme or the other. Barnes calls us to neither extreme, but to be both serious and cheerful. It is worth being aware which direction we naturally move towards, so that we might be able to correct ourselves. To those of us inclined to be more serious, we need to be exhorted not to forget joyfulness and cheerfulness. To those of us inclined to the other extreme, we need to be exhorted to more serious thought, reflection and conversation.
This is worth thinking about because our demenour not only effects us, but also has a lasting impact on those around us. What does a joyful seriousness or a grave cheerfulness look like? What impact would such a demeanour have on those around us? I don't pretend to have all the answers, but it is something worth thinking about, and is perhaps something that we've not thought much about before.