H.G. Wells once wrote an essay on a tribe of people he called the "Goodness Sakers". These were the folks who when they saw something that needed to be done, or when they saw a social evil, or detected some moral shortcoming, would stand around and wring their hands and say, "For goodness sakes, why doesn't someone do something about this?"

I know a lot of "goodness-sakers". They're always saying "for goodness sake, something ought to be done." But they never get around to sharing in the doing of it. So the obvious truth of the parable is that unfruitfulness is not allowed God's vineyard. Uselessness is a sin because it means that when we are useless we fall short of God's intention for us.