The Mekhilta draws a legal principle from a seemingly mundane phrase about safekeeping. When the Torah discusses items entrusted to a guardian, it mentions "money or vessels." A simple pair of examples — but the rabbis saw a hidden rule embedded in the juxtaposition.
Money, by its nature, is counted. You know exactly how many coins you handed over. Vessels, similarly, are the kind of objects that tend to be individually identified and numbered. From this pairing, the Mekhilta derives a sweeping legal principle: any claim that is not susceptible to measurement, weighing, or counting is not a valid legal claim at all.
This ruling shaped an entire branch of Jewish civil law. If you entrust something to a guardian and later claim it was lost or damaged, you must be able to specify exactly what you gave and in what quantity. Vague accusations — "I think he lost some of my grain" or "my pile of wood seems smaller" — cannot form the basis of a lawsuit. The Torah demands precision in legal matters, and the Mekhilta locates that demand in these two small words.
The deeper insight is about how God structured the legal system to protect both parties. The plaintiff must be precise enough to prove a loss. The defendant must face only claims that can be verified. By anchoring the law in countable, measurable, weighable things, the Torah eliminates the chaos of subjective grievances and builds a system where justice can actually be determined. Two words in a verse about safekeeping — "money or vessels" — became the foundation for centuries of commercial law.