VANITY IS FUTILITY.
According to the book of Ecclesiastes, everything is vanity because the good and the evil, the wise and the foolish, the lucky and the unlucky, the haves and the have-nots all turn to dust in the end. If you're honest about it, that's a hard point to refute.
Saint Paul puts it this way, "If Christ has not been raised, then our preaching is in vain and your faith is in vain. If for this life only we have hoped in Christ, we are of all people most to be pitied" (1 Corinthians 15:14,19). In other words, he is as honest as Ecclesiastes if not more so. But then he goes one step further.
He says Christ has been raised. In honesty he has to say that too, because on his way to the city of Damascus one day he experienced it. That being so, he suggests, not even death is futile. That being so, not even life is in vain.