At the request of a Marxist reader who wants "the basic concepts of magic" explained ... well, I started writing something along these lines. But then I got distracted and ended up explaining the basic concepts of Marxism for occultists - it seemed that I had to do it this way first. So, apologies - "Magic 101 for Marxists" will be coming. But first...
Marxism is a materialist philosophy - the starting and ending point of our ideas is the actual, physical, real, dirty world. We use this world in contradistinction to "idealism" - the concept that ideas are the fundamental building blocks of reality. But the essence of Marxist materialism is that the real world and the "sphere of ideas" are intimately connected. "Vulgar materialism" - that is, the hard-core sceptic view of reality - carries on Descartes' hard-and-fast dividing line between physical reality and ideas. This concept that ideas are totally independent of reality is in fact another, stupider, kind of idealism, in which ideas just kind of float around in a disembodied state and operate by their own laws.
As Lenin said, "intelligent idealism" - accepting that ideas shape reality - is closer to Marxism than the "vulgar materialism" which, as we've shown above, is actually a vulgar kind of idealism under an assumed name. Marxists accept that material reality shapes the ideas in people's heads. But that when people act according to different ideas, then they can change material reality. The connection between matter and ideas is action.
Marxists are dialectical materialists. The "dialectic" can be summed up in a single idea: that everything is in a continual process of flux and change, that everything contains within it the seeds of its own destruction and evolution into something different. Opposed to the vulgar materialist worldview in which the world contains a number of fixed, isolated objects, for the Marxist the world is made up of processes whereby things evolve over time and relations between things. A Marxist is more interested in the direction in which something is going than where it is at any given moment - Trotsky noted that in this, dialectical logic is different from formal logic in the same way that calculus is different from arithmetic. Marx got this idea from the German idealist philosopher Hegel, who seems to have picked it up from the Greek Heraclitus - it's a surprisingly common idea in even Western philosophy, let alone the rest of the world. See for example the extract from Crowley's translation of the Tao Te Ching, a few posts down from here.
The basis of Marxist philosophy can be summed up thus: the whole world and everything in that world is in a continuous process of change and flux. But human consciousness was born in the struggle to change the world according to our will. Marx, writing at the time when industrial capitalism was booming all over the world, saw this as the first time when a truly global human civilisation, which could not only gain control over the physical world but over its own evolution, was possible. But he also saw that capitalism - while smashing the old, static feudal and traditional civilisations - was a "Sorceror's Apprentice" that couldn't control the powers that it had summoned up.
Marx saw that the division between mind and matter in the philosophy of the rulers of his era was echoed in the division between the capitalist class - who directed production for their own private benefit - and the working class, who actually carried production out. Consciousness belonged to one group of society - the power to actually do things to a completely different group. Thus, the very basis of capitalist society at the same time summoned up great powers and made it impossible for humanity or even individual humans to have any control over these powers.
Only when the industrial working class - who actually with their physical labour changed the world on a daily basis - became fully conscious of what they were doing, and took over control of the way in which they created the wealth of the world, could this contradiction be solved. The ascension of the working class to the leadership of society would be at the same time the solution of the split between theory and practice, mind and matter, consciousness and physical reality. It was necessary for the real history of humanity to begin - a history when a self-conscious species would take over responsibility for its own future and the future of the planet and perhaps the universe. The sole important amendment that modern Marxists would make to this is to make it clear that low-paid white-collar workers - who shift information rather than steel for a living - are also going to have to be part of this process.
In summary, then: Marxism is the philosophy and science of the human race coming to full self-consciousness and responsibility. Against us stands the self-interest of the ruling classes of the world, who have massive power over other humans but no real power over the world they live in. These people, for example, couldn't solve global warming if they wanted to, because the measures they'd be forced to take would destroy their own self-identity as rulers of the world. Marx didn't forsee the possibility of ecological collapse, but he certainly had in mind "civilisational collapse" of the kind that happened to ancient Rome. Only a self-conscious world working class could save humanity from such a fate - precisely because, as he famously said, it had "nothing to lose but its chains".
So what stops the workers of the world from achieving this? On one hand, the rulers are not ashamed to torture, destroy, kill, imprison and use any and all kinds of violence to protect their power. But in the advanced Western countries right now, the control of the rulers of the world is imposed by ideology. And this is where Marxism and occultism really begin to share a frame of reference.