T-Rex: Monotheism pretty much has it all together.
T-Rex: Just ONE GOD!
T-Rex: And according to orthodoxy, Muslims, Jews, and Christians all actually worship the same god! So together!
Utahraptor: That is true in a technical sense...
Utahraptor: But it's also kind of like saying all Unix users run the same operating system.
T-Rex: It's a God system!
T-Rex: I know this!
The author writes:
Utahraptor's analogy just gets deeper and deeper the more you think about it.
It is universal among Orthodox Jewish rabbis that Jews do indeed worship the same god as Muslims. However, the prevailing opinion is that we do not worship the same god as most if not all Christians, because of the complicating factor of the Trinity. Virtually all Jewish religious authorities consider Catholicism to be polytheistic, while some minority opinions differ with regard to certain Protestant or other sects.
The discussion of exactly which other religions qualify as monotheistic is an entire branch of Jewish law with practical applications. For instance, religious Jews are allowed to freely enter and even pray in a mosque - but are supposed to be ready to give their lives rather than even set foot in a church.
In my defence, Wikipedia says:
Traditionally, both Judaism and Christianity believe in the God of Abraham, Isaac and Jacob.
However, as Daniel points out, it also confirms:
Christianity posits that God exists as a Trinity; in this view God exists as three distinct persons who share a single divine essence, or substance. [...] By contrast, Judaism sees God as a single entity, and views trinitarianism as both incomprehensible and a violation of the Bible's teaching that God is one.
From my outsider's point of view, it seems that:
I can see that each religion claims their God is fundamentally different from that of the other religion - but on the other hand it's the same source material they're both deriving from.
It's a bit like two different people describing New York City and Gotham City. They're very similar, and even have a lot of the same landmarks, so you might think they're talking about the same place. They're both clearly inspired by the same source material, but one of them is mentioning things like Oswald Cobblepot and Sal Maroni, who don't really exist. Which religion is getting it wrong, of course, is the big debate... (if in fact either of them is getting it right - the other might be talking about Lois Lane and The Daily Planet...)
I think in short, as with many things about religion, it's complicated to the point of self-paradox.