The context for the article was the campaign of the German Jews for political emancipation. This must have been a subject close to Marx's heart, given that he was himself not only Jewish but descended from a family of rabbis.
Marx's friend Bruno Bauer had argued that Germany's Jews could achieve true freedom only by renouncing their Judaism. But - Marx argued - it was no good attacking religion. Religion was the wrong target. Marx observed that even officially secular states like the USA had ended up remaining de facto religious. He deduced from this that there must be something radically defective about the modern capitalist state itself. And if the current form of the state was abolished, religion would go with it.
The source of the problem was that the liberal revolutions of the 18th and 19th centuries had brought about only political equality. They had not removed wider social distinctions - and the persistence of these social distinctions, which included religious affiliations, were more important than the fact that men now increasingly had legal-constitutional rights such as freedom of speech and the vote. This was demonstrated by the fact that the Jews wielded great social power even though they still lacked political rights.
This leads on to the real interest of this piece - its repetition of the classic tropes of European antisemitism. Jews were grasping and materialistic. Their true god was money. They had acquired disproportionate economic influence and had infected the culture of Christian countries. A socialist society would accordingly be a post-Jewish society. Not many present-day Marxists would be comfortable with their intellectual godfather coming out with stuff like this:
What is the secular basis of Judaism? Practical need, self-interest. What is the worldly religion of the Jew? Huckstering. What is his worldly God? Money.
The Jew has emancipated himself in a Jewish manner, not only because he has acquired financial power, but also because, through him and also apart from him, money has become a world power and the practical Jewish spirit has become the practical spirit of the Christian nations. The Jews have emancipated themselves insofar as the Christians have become Jews.
Money is the jealous god of Israel, in face of which no other god may exist.
In its perfected practice, Christian egoism of heavenly bliss is necessarily transformed into the corporal egoism of the Jew, heavenly need is turned into world need, subjectivism into self-interest. We explain the tenacity of the Jew not by his religion, but, on the contrary, by the human basis of his religion – practical need, egoism.