I think what Marx meant is somewhere between what Joanna and Shane say he meant and what Chris says he meant. He says both (or Engels does) 'freedom is the recognition of necessity' (quietistic, comparable to Zen), but also 'freedom is the leap from necessity' (in which case he does mean something like the 'self-deification of man', or what Lukacs called 'societal self-determination', or, until the phrase was ruined, 'social democracy').
Seen in formalistic terms, of course you cannot leap from necessity (anymore than necessity needs to be recognised). But Marx says these rigid oppositions fall away the closer you get to practical life. His example was the oceans, which at one level of development are insurmountable barrier, but at another, most convenient means of communication. As he sees it there is an ongoing passage from objective condition, into subjective action, which in turn creates tomorrow's objective conditions.
It is not surprising from Marx's view that we should constantly try to diminish our responsibility for making the social world and imagining that it is made for us, because we lose sight of the subjective actions that lay the ground for the modern world, and act in something like what Sartre called 'bad faith'. But a moment's reflection makes it clear that modern society could not exist as the simple realisation of objective conditions or natural laws.