Why does the author repeatedly call these perplexing realities 'vanity'? It's more than just a word; it's a conclusion about the limits of earthly understanding.
The repeated use of the word 'vanity' (or 'futility,' 'meaninglessness') is the author's way of labeling these troubling observations. He's not saying these events are insignificant, but rather that they reveal the inadequacy of seeking ultimate meaning or a perfect system of justice solely within the confines of earthly existence.
When we see good people suffer and bad people thrive, and try to build our entire life's philosophy on the assumption that earthly rewards and punishments always align with deeds, we will inevitably hit a wall of confusion and despair. The author concludes that this aspect of life, when viewed in isolation, is indeed 'vanity' – a deceptive and ultimately unsatisfying basis for life's meaning.