The law of value is an objective law of commodity production and is the fundamental regulating law of capitalist commodity production. It states that the value of a commodity is determined by the amount of socially necessary labor time in its production. Under capitalism where anarchy of production and competition between laborers for wages and between capitalists for market shares hold sway in society, the law of value acts as a spontaneous regulator of production. Under the capitalist mode of production, the law of value directs labor and capital to areas of greater profitability.
The law of value is the economic law of commodity production and exchange. The basic content of this law is this: The value of a commodity is determined by the socially necessary labor. Commodities must be exchanged according to their values. That is, there must be equivalence in exchange. Wherever and whenever the conditions of a commodity economy exist, the law of value has a role to play. Marx said, ‘In the anarchic constantly changing trade relations of private labor products, the socially necessary labor time for their production forcibly clears its own path as a regulatory law of nature, just as the law of gravity forcibly clears its own path when a house falls on a person’s head.’ In other words, in commodity exchange, although because of the influence of the supply-demand relation the proportions in which commodities are exchanged may change continuously so that the socially necessary labor (the value) embodied in two commodities being exchanged may not be exactly equal, in the long run, commodity exchange necessarily involves equivalence in exchange. The values being exchanged must be identical.
(China Book Project, Fundamentals of Political Economy, edited with an introduction by George C. Wang, 1977.)
https://www.marxists.org/history/erol/china/fundamentals.pdf
Surely there is a way to say this in a way that the practical revolutionaries of today can understand.