This is one of my favorite allusions. In Greek mythology, Sisyphus was a king of Corinth who committed a variety of misdeeds on earth, and was relegated to punishment in Tartarus.
His punishment was that day after day, he was compelled to push a large boulder up a steep hill. Every time, as soon as he got it to the top, it rolled down again. Thus, he had to begin pushing it up again and his labor never ended. So if you are stuck in some sort of labor that seems both endless and fruitless, you can refer to it as a labor (or boulder) of Sisyphus, or as a Sisyphean task.
I think this particular allusion can be useful in churches of Christ as we discuss the idea of "restoring" the early church. When I took John Mark Hicks for Restoration Theology, the point was made that we can never really "restore" the early church. Restoring should be thought of as an ongoing process toward which we are always working. I personally disagreed with that, and I argued that while we might not be able to attain moral perfection, to restore the doctrines and practices of the early church is something I believe is somewhat attainable. I stated that the Restoration Movement is in fact a boulder of Sisyphus if it's not possible to ever reach what we're working towards.
In the end, I think that the selection of a better metaphor (at Dr. Hicks' prudent suggestion) helped to clarify. Education seems to be a better comparison. While we can never have exhaustive knowledge of all things, we can learn and mature in a very real sense, and we can stand on the shoulders of those who've gone before us. Because of doctrinal intricacies and cultural differences, it might not be possible for us to be a facsimile of the early church, but we can--and I think we have--made good strides in returning to basic Christianity.