In our daily relationships with people, cheerfulness, which we show by smiling at the right moment or by being pleasant to those we encounter, opens the door for many souls who are on the point of closing themselves to any sort of dialogue or understanding. Cheerfulness encourages people and helps them in their work, and assists in overcoming the numerous reverses that life sometimes brings. A person who habitually lets himself succumb to gloominess and pessimism and does not struggle to overcome it straightaway, will be a dead weight, something of a morbid liability for others. Cheerfulness enriches other people, because it is the expression of an interior richness that is not improvised, stemming as it does from the deep conviction that we are, and recognize that we are, children of God. Many people have found God through the joy and the peace emanating from Christians they come in contact with.
from In Conversation with God by Francis Fernandez Volume 3 p.37