I'm Christian, and I believe that the abrahamic religions worship the same entity. "The lamp is different; the light is the same." Now what? :-)
Yes, many Christians will consider that Muslims worship the same God. On the other hand, I grew up in the American South, and I can assure you that the sentiment is not universally shared down here.
You are right nominally; the person you're replying to is right in terms of doctrine. Otherwise, you would say you were Muslim (or some pan-abrahamic variant) and not Christian.
Pope John Paul II has said the fact that Christians and Muslims worship "the One and same God" is a factor that draws the two communities together and lays the basis for love and cooperation between the two communities of believers.
Really? Catholics, Anglicans, most "mainline" Protestant churches are doctrinally copacetic with the notion that jews, muslims and christians alike all worship the god of abraham. This was not always so, of course, but it turns out that ecumenicalism is a pretty smart idea.
To your point about Theseus -- https://en.wikipedia.org/wiki/Apophatic_theology is germane here. In this way of thinking, definitionally we can only agree on what God isn't, not what it is.
Sure, but the criterion for sameness is what matters. I see this as cultural and historical sameness, not doctrinal; the doctrines of the Abrahamic religions certainly do not agree on the fundamentals.
I also don't view it as apophatic, as I acknowledge both positive and negative claims are possible. I just think it comes down to the criteria of "sameness" and so it's ultimately an ambiguous question, and one must specify what is effectively being asked. Depending on the actual question, both your answer and others can work.
If you're too strict about sameness criteria, it's difficult to agree on what, like, pants are, and we wind up at the relatively trivial solipsism arguments that get boring pretty quick.
If you go back far enough, of course, the doctrines of the abrahamic religions _do_ agree on the fundamentals. "God made stuff, God is on our side, act accordingly." The procession of covenantal relationships throughout history (with noah, abraham, issac, ishmael, jacob, john, jesus, mohammed, etc. etc. ) continually reinterpret what that means for people, but the basics are something everyone can break bread over.
> ... fundamentals ...
If I may butt in. That's one such essential message of these religions, that we are all the same and equal. Yet their essence is to define the respects in which to compare for equality and in those they do differ substantially. The primary difference is the question of authority, which has differing answers IMHO, and I believe that's the same question as the GP was asking.
And so you pretty quickly end up with fundamentalism, except that they all cannot agree on whose fundamentalism, whose authority, whose definition of failure to accept.
abraham?
Meaning, if you asked a Christian whether he and a Jewish follow believe in the same god, he would say yes. The Jew would probably say No (I once heard a Jewish man refer to the New Testament as "that appendix").
By the same token, a Muslim would insist that he follows the same god of Abraham, Moses, Jesus, etc. A Christian, however, would say that he does not.
See also the Druze and Bahai'i faiths, which draw upon an extend the Abrahamic faiths.