Well, without Judaism you don’t have either Christianity or Islam.
This. Someone* once said that Christianity is merely the most successful Jewish heresy, and Islam the most successful Christian heresy. In that sense, Judaism is absolutely a major religion, although the vast majority of its adherents are heretics.
*No cite. Can’t remember where I read that, doesn’t matter anyway.
You do realize that your post stating “… or you specify it as coming through Christianity and Islam, which would be a fair position” and mine that you are responding to, complaining about not having read your posts, were simulposted?
Even if not I would still ask for clarification. I mean that Christians and Muslims today are aware of Judaism and of its influence on their own faith, think of it as a major part of their own history, and think that interactions with Jews today are of import to their faith and culture. Not just by way having been the antecedent of. Most Muslims and Christians know about Judaism (whether or not what they know is accurate or not is another issue).
The big four are unquestionable: Christianity; Islam; Hinduism, and Buddhaism. In the next rung you have: the Sikhs at 25 million, almost all (90%) in India; Shintoism at 3 million almost all in Japan; Taoism at 8 million almost all in China; and Judaism at 14 million, historically pretty wide spread, a known entity (at least in sterotype) to almost all Muslims and Christians, and of outsized impact in Western culture.
So again, by numbers you’d have to go with the number 5 spot to the Sikhs currently. That said before the Holocaust, use 1900, Jews were 0.68% of the world population, at 11.2 million (previous cite), while the Sikhs with their 500 year history had reached2.2 million at that time. Even as recently as 1971 the Sikh population was just 10.4 million, compared to 12.6 Jews. The greater number of Sikhs than Jews worldwide is a recent item, over the last few decades tops. Again, they are concentrated in one country (India), in one region of one country (mostly Punjab), and not a majority even in that one region. It seems like a wonderful faith with much to offer but to place it as one with great impact on the rest of the world’s cultures, to posit that its several decades of largish numbers in one region places it as more impactful than Judaism, seems unwarranted.
So #5 does seem to belong to Judaism, based on historic numbers and spread. Still a fraction of adherants compared to the big 4. It’s being mentioned (rather than stopping at 4) is still more of a historic nod to its relevance to the big 2, Christianity and Islam, and a function of, as noted by Alessan, its relevance to those who write those books.
One other point that Judaism has going for it is that it’s the official religion of a country. Can Jainism or the Sikhs make that claim?
If you accept the argument that Judaism should get “credit” for its influence on other religions, how about Zoroastrianism? It influenced Christianity and Islam as well. And it was a historically major religion politically before being supplanted by Islam. Plus Queen had fourteen albums that went number one.
You misunderstand the point. Or you are whooshing. Hard to tell which.
The point is not historical “credit” for that which happened many hundreds or thousands of years ago; the point is current members/leaders of those faiths across the world are aware of those relationships and see both the compare/contrast as vital to how they define themselves, and relations with today’s Jews, no matter their small numbers, as an item of current importance (no matter if that is a conflictual or cooperative relationship).
Even China has multiple academic centers devoted to Judaic studies. Any Chinese departments of Sikh studies? Not that I can find. I think the Chinese mainly think of the Sikhs as having been Britain’s enforcers during the Opium War and perhaps for the Sikh led invasion of Tibet. Not as a major religion. The Sikhs, even with their currently (and fairly recently) large absolute population size are of significant cultural impact only in Punjab and of minor cultural impact to India as a whole. They are not and have not ever been of major impact on the culture of the rest of the world outside of that one country, West or East.
To be fair, the “world religion” status of Buddhism, and to some degree of Christianity and Islam, involves lumping together a great number of different religious sects that share some common myths and labels. Not all Buddhism is Thai-style Theravada by a long, long way.
And Hinduism is a funny concept in its own way. I know it’s not quite, “Whatever religion is found in India that’s not Islam.” Not quite. But it’s a tradition, a respectable tradition to be sure, that encompasses a lot of different philosophies.
Judaism helps explain the backstory of Islam, as Hinduism may help explain Buddhism. Or not.
Perhaps we should also cover Anatolian mystery religion and the cult of Hercules to help explain Christianity. 
Or more seriously, Zoroastrianism and Manichaeanism, however little extant remains of them.
I think that’s a good question. Perhaps part of the difference is that for quite a while now, Jewish people have around the center of the action both geographically and intellectually.
If Jewish people had faded into relative obscurity a couple thousand years ago, I doubt that Judaism would be seen as a major world religion despite any influence on Christianity or Islam. But instead, there has been a significant Jewish presence in a lot of important cities and Jewish people have been very prominent to the current day.
Anyway, if I were making a list of religions which people needed to learn about I would probably include Zoroastrianism.
I’m not whooshing (except for the Freddie Mercury joke). I’m asking for opinions (and offering my own).
Well, probably everyone reading this has at least a little knowledge of Judaism… “Can’t eat pork, religion of Moses,” etc. How many of us know any specific doctrinal points of Sikhism. (Is it even called “Sikhism?” What is the name of the faith? “The Sikh Faith?”)
Sikh thought simply hasn’t penetrated the world market of ideas anywhere near as deeply as Judaic thought.
To follow on brazil84 and Trinopus’s posts:
It’s also the case that Christian communities have been known to convert to the apparent root faith of Judaism* en masse.* And then there’s the case of the Khazars. Judaism has been both widespread and attractive for a very long time.
Absolutely.
The op is however related to another subject that I know has been discussed here before (although damned if I can find it) - most Americans and I suspect most in the world (and not just the West) think that Jews are much more numerous than they are. I don’t think many appreciate how big the gulf in adherent numbers is between those top 4 and Judaism.
So indeed, it may not be top tier in absolute numbers, but it’s definitely top tier in both real and especially perceived continuing influence and visible presence-- even more out of proportion when you consider for how long its dominant forms have not supported proselytizing or claims of universality. Not bad work.
Well, sure, that, too.
Well, Singapore, arguably.
Monaco.
The Vatican…
What, you mean you guys aren’t ranking religions by their relative share of Nobel Prize winners?
I see it as a major world religion because it is recognized as a fetal state of 2 world religions. As such it is part and covered under Christianity and Islam which qualify.
It was this close to being relative share of reggae albums. But Rastafari lost the coin toss.
As I’ve said, that argument seems weak to me. Christianity is a major world religion because of the impact of Christianity. Islam is a major world religion because of the impact of Islam. I don’t see how Judaism can be regarded as a major world religion because of the impact of two other religions.
It’s not because of the ‘impact’ but because they are the same, just different stages of development.