Alongside our charity we have to also show the world our joy. This is the joy the Lord promised us at the Last Supper. It springs from our effort to put aside personal worries and enter into friendship with God. Joy is essential to the apostolate. Who will be attracted by a sad and negative critic or a gloomy complainer? The apostolic fruitfulness of the first Christians was the result, in good part, of their joy at being the heralds of the Good News. They were the messengers of the One who had brought salvation to the world. They shone forth as a happy people in the middle of a world in anguish. Their happiness spread abroad their faith in Christ. It was a special gift that they shared in their families and among their friends ... at every moment, since it was their very reason for living.
Christian joy has a solid foundation in the reality of divine filiation. This is the recognition that one is a son or daughter of God at all times. As Chesterton suggests, it is joy not because we are in the right place, but because we are in the wrong place. We were lost, but Someone has found us and is leading us home. It is joy not because we are alright - we are not - but because Someone can put us right. Christian joy comes from facing up to the one really sad fact of life, which is sin; and countering it with a joyful fact that is even realer and stronger than sin: God's love and mercy.
Let us ask ourselves whether we reflect Christian joy in our ordinary life. We have so many reasons for being happy: the wonder of our divine filiation, the comfort of divine mercy, the knowledge that we are on the road to heaven ... , the joy of being able to receive communion so often! The first step towards bringing others to the ways of Christ is for them to see you happy and serene, sure in your advance towards God
In combination with the joy and charity of Christ, we have to be able to express the truths of the faith which will make others happy. Only convinced Christians have any chance of convincing others. Half-convinced Christians won't even half-convince anybody. They won't convince at all.
from In Conversation with God by Francis Fernandez Volume 5 pp.145-146