From Dietrich Bonhoeffer’s sermon preached on July 20, 1930, and later translated and published in his Works (10:575):

Rejoice always (1 Thess. 5:16). Are we to rejoice in the manner of that crowd of people we see searching for “gaiety” each evening in the great streets of Berlin? Certainly not; they are like moths that dance and flutter around the light at night until it burns them up. Christian joyfulness has nothing to do with such gaiety. Nor does Christian joyfulness have anything to do with some pleasant diversion after a gray workday. Everything we generally call joyfulness, even joyfulness that is not entirely illegitimate, is prompted by things that are transitory like everything else in the world, things that in their very transience take our joyfulness away from us when they pass away, leaving behind only melancholy recollection.

Where is all that joyfulness that our personal or professional life has brought us in pleasant hours? Irrevocably gone. Forget the past; beautiful as it may have been, it can never return again the way it was.

Today’s text, however, speaks about a happiness that abides, one that lasts a lifetime, one that does not dissipate when those happy times are over, one that endures because it has its foundation where there is no more growth or decline, namely, in the fatherly heart of God. Here you find anything but wild boisterousness and desire, which, after all, are merely the anxious grasping for things in this transitory world. Here we stand as whole persons before God the Father; our hearts are filled with a happiness never known before, a happiness that seeks to seize and change our lives from within. This joyfulness has only one enemy, namely, the care and sorrow that subjugate people to this world and make them fearful. A person should be joyful, not fearful, since above all that happens there is a heaven, an eternity, a Father.

But with my tormented, heavy heart, where does my joyfulness come from, where do I find it?

Go outside and see how children play and rejoice and are happy; see how the birds of the field fly high up to heaven and are joyous in the sun. Watch them, and then watch them again and again, and then rejoice with them, become like them, like a child that is joyous in its father’s garden. Above all, however, turn to him who loved the children and birds and flowers and who himself was a joyous child of his Father and who has become your redeemer: to Jesus Christ. In him the Father himself encounters you; in him God comes close to you, and in him one thus finds the foundation and source of all joyfulness. Rejoicing means enjoying God’s nearness in Christ Jesus.