Marx wrote about jews quite a bit, despite having jewish blood or ancestors.
- Was Marx an anti-semite?
The Jewish Question is a criticism of Bruno Bauer, who argues that the emancipation of Jews is subordinate to the emancipation of mankind:
Bruno Bauer replies to them: No one in Germany is politically emancipated. We ourselves are not free. How are we to free you? You Jews are egoists if you demand a special emancipation for yourselves as Jews. As Germans, you ought to work for the political emancipation of Germany, and as human beings, for the emancipation of mankind, and you should feel the particular kind of your oppression and your shame not as an exception to the rule, but on the contrary as a confirmation of the rule.
Why should the German be interested in the liberation of the Jew, if the Jew is not interested in the liberation of the German?
By its very nature, the Christian state is incapable of emancipating the Jew; but, adds Bauer, by his very nature the Jew cannot be emancipated. So long as the state is Christian and the Jew is Jewish, the one is as incapable of granting emancipation as the other is of receiving it.
So Bauer demands that Jews cease to consider themselves as Jews, as a precondition of their emancipation: you are free to be Jews, as long as... you are not Jews. Then the stigma of Judaism, imposed upon you, is unjust and discriminatory; but as long as you remain Jewish, you cannot argue against discrimination, for you discriminate yourselves:
Bauer, therefore, demands, on the one hand, that the Jew should renounce Judaism, and that mankind in general should renounce religion, in order to achieve civic emancipation. On the other hand, he quite consistently regards the political abolition of religion as the abolition of religion as such. The state which presupposes religion is not yet a true, real state.
Marx then, having expounded Bauer's positions, states:
At this point, the one-sided formulation of the Jewish question becomes evident.
It was by no means sufficient to investigate: Who is to emancipate? Who is to be emancipated? Criticism had to investigate a third point. It had to inquire: What kind of emancipation is in question? What conditions follow from the very nature of the emancipation that is demanded? Only the criticism of political emancipation itself would have been the conclusive criticism of the Jewish question and its real merging in the “general question of time.”
Because Bauer does not raise the question to this level, he becomes entangled in contradictions. He puts forward conditions which are not based on the nature of political emancipation itself. He raises questions which are not part of his problem, and he solves problems which leave this question unanswered. When Bauer says of the opponents of Jewish emancipation: “Their error was only that they assumed the Christian state to be the only true one and did not subject it to the same criticism that they applied to Judaism” (op. cit., p. 3), we find that his error lies in the fact that he subjects to criticism only the “Christian state,” not the “state as such,” that he does not investigate the relation of political emancipation to human emancipation and, therefore, puts forward conditions which can be explained only by uncritical confusion of political emancipation with general human emancipation.
And then he poses the correct question, cleaned up from Bauer's confusions:
If Bauer asks the Jews: Have you, from your standpoint, the right to want political emancipation? We ask the converse question: Does the standpoint of political emancipation give the right to demand from the Jew the abolition of Judaism and from man the abolition of religion?
And then proceeds to clarifying the relation between religious emancipation and what he calls human emancipation:
The political emancipation of the Jew, the Christian, and, in general, of religious man, is the emancipation of the state from Judaism, from Christianity, from religion in general. In its own form, in the manner characteristic of its nature, the state as a state emancipates itself from religion by emancipating itself from the state religion – that is to say, by the state as a state not professing any religion, but, on the contrary, asserting itself as a state. The political emancipation from religion is not a religious emancipation that has been carried through to completion and is free from contradiction, because political emancipation is not a form of human emancipation which has been carried through to completion and is free from contradiction.
The religious citizen is politically free (ie, free to follow the superstition of his own choice without fear of political retaliation) when the State is free from religion. But his political freedom of religion, or even from religion, is not his emancipation from superstition, from religion, as such. Religion ceases to be a State issue, a political issue, but becomes a private, civil, issue, and continues to enslave men and women at that level, while the State is now free to play the role of Pontius Pilatus.
The Jewish citizen can now go the Sinagogue and worship the Abrahamic God in his particular way, without fear of being burnt at the stake by the Christian Leviathan; but he continues to have to abstain from pork, under the fear of whatever punishment YHWH unleashes unto those who so do - and under the fear of whatever merely social, cultural punishment the religion prescribes for such sinners.
Therefore, we do not say to the Jews, as Bauer does: You cannot be emancipated politically without emancipating yourselves radically from Judaism. On the contrary, we tell them: Because you can be emancipated politically without renouncing Judaism completely and incontrovertibly, political emancipation itself is not human emancipation. If you Jews want to be emancipated politically, without emancipating yourselves humanly, the half-hearted approach and contradiction is not in you alone, it is inherent in the nature and category of political emancipation. If you find yourself within the confines of this category, you share in a general confinement. Just as the state evangelizes when, although it is a state, it adopts a Christian attitude towards the Jews, so the Jew acts politically when, although a Jew, he demands civic rights.
This is the spirit of the book, which can be found at the Marxists Internet Archive. We can of course discuss whether this is anti-semitic, from an informed point-of-view. But we should not take a few sentences out of context, in order to demonise the author. Yes, the book contains the sentences quoted in the OP, and others of similar gist; but they are there not to stand by themselves, but as part of a much more complicated reasoning, in which Judaism is not a race, nor merely a religion, but a especial role necessary for the functioning of the "Christian" society.
Marx's views were arguably anti-Semitic:
What is the worldly religion of the Jew? Huckstering. What is his world god? Money.
— Marx, „On the Jewish Question“, 1844; (ref. Francis Wheen — „Karl Marx: A Life“, 2001)
I think it is fair to say that Marx looked at all religions as a method of pacification of the masses. As far as Judaism in particular, for the time and place, there was a predominant antisemitic sentiment. There seems to be some particularly poignant information regarding Karl Marx's father, Heinrich Marx.
H. Marx having lived during the post Napoleonic era of German control of the Kingdom of Prussia, experienced a strict Lutheran based social environment. Antisemitic rhetoric for that era would not be uncommon. So much so that Heinrich Marx, whose father was a rabbi, converted from the religion. I don't mean to say this is definitively an account of what occurred, nor was your question about why he may have been an antisemite.
P.S. This was an interesting question. I really enjoyed delving into the "Napoleonic Jewish emancipation" and about Heinrich Marx as well.