So becoming missionaries to foreign lands, giving up your own lifestyle to spread the "Good News" of Jesus The Messiah is just "sitting on their elbows, waiting for the Messiah to come"? You must know very little about Christians and their devotion to their God and Christ if you think that we just sit on our elbows, waiting for the Messiah to come. How pitiful.
However, people who think the Messiah is just around the corner and therefore they don't have to concern themselves with the everyday, Earthly lives of themselves and others are wasting their lives.
That's not something exclusive to Christians. Jews have done their share of it as well. Many of those who followed Sabbatai Zevi, to the exclusion of real lifes, for example.
And now, I really need to be planting trees.