Every era has its fitting ideologies and theories.
Take Marxist economics that emerged with industrialization, for example.
The past 100 years of economic history is explained by this economics alone, and all scholars fitted history into Marx's theory.
The labor theory of value forms the foundation of Marxist economics.
Marx's labor theory of value emerges with one topic.
Assuming a product's price is its production cost.
Where exactly does profit come from?
Many factors go into producing this product like raw materials, wages, production costs, facilities, but no factor cleanly explains this 'profit' generated when the product sells.
Here the labor theory of value states:
Labor power creates profit.
Just as a farmer creates a year's profit through good farming, the labor theory of value says labor power is profit.
Truly a simple yet intuitive theory.