Like political economy, philosophy & religion cannot merely be done away with in thought (or through atheism), but through the practical reconcilation Marx spoke of through communism and the abolition of private property. This is why he called it the riddle of history solved. Now, I'm nearly finished, but religion also shares properties of capital for Marx:

(...) we must have recourse to the mist-enveloped regions of the religious world. In that world the productions of the human brain appear as independent beings endowed with life, and entering into relation both with one another and the human race. So it is in the world of commodities with the products of men’s hands. This I call the Fetishism which attaches itself to the products of labour, so soon as they are produced as commodities, and which is therefore inseparable from the production of commodities.

https://www.marxists.org/archive/marx/works/1867-c1/ch01.htm

"Fetishism" here is not the typical way in which schoolgirl skirts arouse heterosexual men, but in an inanimate object that appears to be inhabited by a religious spirit. Man creates religion and bows down to it in thought. In reality, products are produced and appear to immediately be commodities, often owned by someone who is not the one who produced it, and whose overproduction 'causes' crisies and 'forces' people to go homeless or struggle to pay for food & the likes, despite that, obviously, it is all by our own hands.

The religious world is but the reflex of the real world. And for a society based upon the production of commodities, in which the producers in general enter into social relations with one another by treating their products as commodities and values, whereby they reduce their individual private labour to the standard of homogeneous human labour – for such a society, Christianity with its cultus of abstract man, more especially in its bourgeois developments, Protestantism, Deism, &c., is the most fitting form of religion. (...) The religious reflex of the real world can only then finally vanish when the practical relations of every-day life offer to man none but perfectly intelligible and reasonable relations with regard to his fellowmen and to Nature.

Were the relations of humanity transparent and recognizable, we would not need special experts (like priests/economists/philosophers) to 'explain' them to us or what we are like: they would be immediately intelligible. At the end of Capital's first chapter, Marx describes communist society through the section on Robinson Crusoe's labor which is directly produced for his needs and is immediately understandable.

Now, I would always recommend people read "On The Jewish Question" themselves, but I'll end on these oft-quoted passages:

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.

Very well then! Emancipation from huckstering and money, consequently from practical, real Judaism, would be the self-emancipation of our time.

An organization of society which would abolish the preconditions for huckstering, and therefore the possibility of huckstering, would make the Jew impossible. His religious consciousness would be dissipated like a thin haze in the real, vital air of society. On the other hand, if the Jew recognizes that this practical nature of his is futile and works to abolish it, he extricates himself from his previous development and works for human emancipation as such and turns against the supreme practical expression of human self-estrangement.

https://www.marxists.org/archive/marx/works/1844/jewish-question/

There's a line in the great Cassavetes movie "The Killing Of A Chinese Bookie" where one gangster opines that Karl Marx was wrong, and it is not religion that is the opium of the people, but money. "Money is God." A great line, but one I was always extra-amused by because Cassavettes didn't understand that Marx would have also agreed with that. One cannot simply mandate atheism without knowing where religion comes from and subsequently how to abolish it. (Which, obviously, does not mean by violence, but through it practically becoming superfluous.)

For a less abstract example of all of this, here is, lastly, Lenin explaining the attitude of the workers' party towards religion:

(...)Engels insisted that the workers’ party should have the ability to work patiently at the task of organising and educating the proletariat, which would lead to the dying out of religion, and not throw itself into the gamble of a political war on religion.

We must know how to combat religion, and in order to do so we must explain the source of faith and religion among the masses in a materialist way. The combating of religion cannot be confined to abstract ideological preaching, and it must not be reduced to such preaching. It must be linked up with the concrete practice of the class movement, which aims at eliminating the social roots of religion. Why does religion retain its hold on the backward sections of the town proletariat, on broad sections of the semi-proletariat, and on the mass of the peasantry? Because of the ignorance of the people, replies the bourgeois progressist, the radical or the bourgeois materialist. And so: “Down with religion and long live atheism; the dissemination of atheist views is our chief task!” The Marxist says that this is not true, that it is a superficial view, the view of narrow bourgeois uplifters. It does not explain the roots of religion profoundly enough; it explains them, not in a materialist but in an idealist way. In modern capitalist countries these roots are mainly social. The deepest root of religion today is the socially downtrodden condition of the working masses and their apparently complete helplessness in face of the blind forces of capitalism, which every day and every hour inflicts upon ordinary working people the most horrible suffering and the most savage torment, a thousand times more severe than those inflicted by extra-ordinary events, such as wars, earthquakes, etc...

https://www.marxists.org/archive/lenin/works/1909/may/13.htm