Oh and one last crucial point!
To marx, he sees machines in production as "constant capital" (that is, the devices which create constant production by repetitious activity), and he sees human labour as "variable capital" (that is, he sees humans as either lowering or increasing profits by economic output, since we can work smarter and harder than what we are assigned for). This perfectly mirrors the relation of the "fixed" base of of production to the "variability" of the superstructure.
But here's the important part. To marx, its within this very variability that he derives his theory of "surplus value" or profit from. So, the reason why human labour creates surplus value is because it is this aspect which is fed back into the productive - man is a thinking creature, and so imbues the dead system of undead motion with his divine spark of creativity, which improves these very machines, at once- in the competition of the capitalist to erase human input, but likewise in his ability to mediate production within his own position. This is why its called "surplus value", because it is the "excessive", "virtual", "abstract" aspect of labour which allows capitalists to reproduce their riches. We are supposedly just replaceable "meat robots", yet we necessitate production and exchange - even in the most bssic example - if no one works, how will they buy the products?
This is also why the tendency for the rate of profit to fall can be simplified as saying that as the superstructure is erased, the function of the base becomes unmasked by naked representation, and so contradictions rise to their highest levels, with unemployment and desperate appeals to the destruction of workers rights (we see this today with the desire to get rid of minimum wage).
So, profit is the extracted surplus of variable capital, which feeds the machine, and seeks to erase the human. The more the human is erased, the more he is awakened to this fact, and revolts. This is progress unto revolution.
"Keynesianism" (an economic policy first implemented after the great depression) has provided temporary solutions for capital to deal with this, but thats a different subject. Hope you learned something!