The proletariat is too weighed down by capitalism to create a culture of its own, including a culture of revolution, without the help of renegade members of the more privileged classes. That's why the workers who banded together to wage a political fight against the hereditary ruling classes recruited Marx (unemployed journalist, son of a minor bureaucrat) and Engels (factory owner) to their revolutionary movement, through which those men achieved their synthesis of revolutionary philosophy and revolutionary action, which proved itself in practice with the century's greatest revolutions (Russian, Chinese, Vietnamese, Cuban), both in a positive sense and in a negative sense when the workers paid for those revolutions' deviations (and those in France, Spain, Germany, Indonesia, etc.) from Marxism.
The "Communist Manifesto" is the greatest single ideological conquest of the labor movement.