I'm sorry, it may not interest you, which is fair, but it is important and he clearly explains it at the end here.

But why does all this matter? Let’s jump off the end of the commodity pin and stop counting the angels there and consider the point of this debate. For me, it’s about showing the fundamental contradiction in capitalism between production for social need (use-value) and production for profit (exchange value). Units of production (or commodities under capitalism) have that dual character which epitomises the contradiction.

For Marx, money is a representative of value, not value itself. If we think that value is only created when selling the commodity for money and not before, then the labour theory of value is devalued into a monetary theory. Then, as mainstream neoclassical economics argues, we don’t need a labour theory of value at all because the money price will do. Money prices are what mainstream economics looks at, ignoring or dismissing value by human labour power – and therefore the exploitation of labour by capital. It removes the basic contradiction of capitalist production (which by the way, our book tries to develop).

And also it leads to a failure to understand the causes of crises in capitalist production. It is no accident that Heinrich dismisses Marx law of profitability as illogical, ‘indeterminate’ and irrelevant to explaining crises and instead looks excessive credit and financial instability as causes. Heinrich even claims that Marx dropped his law of profitability – although the evidence for that is non-existent. If profits (surplus value) from human labour disappear from any analysis to be replaced by money, then we no longer have a Marxist theory of crisis or any theory of crisis at all.

For people who are already principled communists maybe Marxist theory doesn't make that much of a difference anymore, you can find almost infinite reasons to wish to see the heads of a capitalist/a landord and an economist on a pike.

But if you want to engage with other leftists that may agree capitalism is "bad"(because healthcare pls and oh no the planet is burning) but they still resort to mainstream economic BS then it is important for you to understand these details.

In the grander scheme of things it also ties in with how liberal leftists see exploitation. They think giving some little bit of money as charity, or maybe even(as discussed in the article) the differences in wages between global south countries and come to conclusions like "If I help them with money they're less exploited" or when looking at global south workers "oh that person is a tech worker and earns 5x the minimal wage there so he is not exploited".

All those takes are tied to the labor theory of value and if you don't see value in the labour itself but boil it down to monetary theory as MR explains then it leads to all sorts of liberal nonsense you see elsewhere.

It’s extremely funny how so many splits in Christianity can be attributed to minute details like this