In 1 Corinthians 15:50-58 we read:
Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your labor is not in vain in the Lord .
"Labor" is "vain" if it is for no meaningful purpose. "Vain labor" is boring, with "boredom" defined not as having nothing to do, but finding no meaning in what one is doing.
A philosophical example of ultimate, metaphysically vain labor is Albert Camus's "Myth of Sisyphus." Sisyphus, according to the Greek myth, was punished for all eternity and condemned to roll a boulder up a mountain, only to have it roll back down to the bottom when he reaches the top. This happens over and over again and again.
Camus claimed that Sisyphus is representative of the human condition: Sisyphus must struggle perpetually and without hope of success. His labor is absurd. Camus thinks if Sisyphus can accept his absurd labor, then he can find happiness in it.
I think many people view their labor as absurd, and find no happiness in it. Their work lack telos (purpose), and is in vain. But from the Jesus-perspective all labor "in the Lord" is not vain, but meaningful. When what we do emerges out of who we are in relationship with Christ, our entire lives become purposeful. Purposeful, *telic living brings satisfaction.
We are to view God as our Employer. From this God-relational POV redemptive activity can be seen and experienced everywhere. What seem to be vain and meaningless tasks from a human POV take on eternal, missional qualities. This happens, not because of any intrinsic majesty of the task at hand, but as a function of who we are under.
Labor under the Lordship of Jesus, and abound in the work you are doing under God.
*telic - a purposeful or defined action; from the Greek word telos, meaning "end," or "goal"; such as teloscope, literally "to see to the end."
In my new book I talk about prayer as purposeful activity - Praying: Reflections on 40 Years of Solitary Conversations with God.