Imagine having everything stripped away in an instant. Job uses a powerful image to describe the vanishing of his well-being: 'my prosperity has passed away like a cloud.'
The loss Job describes is not a slow decline, but a sudden dissipation. The comparison to a cloud vanishing emphasizes the speed and completeness of his misfortune. What was once solid and visible—his wealth, his family, his health, his honor—is now gone, leaving no trace.
Commentators point out that 'welfare' (or 'salvation' in some translations) encompasses all aspects of his happiness and security. It wasn't just about material wealth, but his entire state of well-being. The cloud imagery is potent because clouds can bring life-giving rain, but they can also disappear just as quickly, leaving the land parched. Job feels that his season of blessing has dissolved into nothingness.