...stating a provably true fact.
What do you do with money once you have it? You trade it for things. You only trade one item for another if the item you are receiving has greater value to you than the thing you're giving up. As such, the item you buy is necessarily worth more to you than the money you're spending on said item.
The act of spending money proves that something is more important to you than money. If you really thought that money was the most important thing, you'd never spend any of it, as you would be trading a valuable item for a less valuable item.