" the Tawrat and Islamic fiqh do not differ than Jewish custom as a whole. "
Come on . . .
They have different calendar.
The Muslims reject the entire Jewish idea of God having given them the land of Israel.
Their dietary laws are different.
The marriage laws are different.
They never had the same concept of a temple.
The circumcision is performed at a different age and with different intent.
There is no concept in Islam of being adopted into the covenant-nation of Israel.
Like I said, the
theology of "who/what is God" is very similar, but everything else in Islamic tradition and Quran, especially
social and
legal, varies greatly as to what similarity it has to the Old and New Testaments.
As to the resemble to Christianity, there is one major point that obviates any resemble and it is this: They reject the Crucifixion. Now, they don't reject it's significance or interpret it differently, no no, they reject that it ever even
occurred.
You mentioned Islam as being built on a mix of paganism and Judaism and to a lesser extent Christianity (which I think may be perhaps simplistic or only partially correct).
(imo) Islam is to
some degree derivate of Gnosticism, I think is perhaps worth adding - that is where they get their pseudo-Docetic Christology.
Compare the Islamic substitution interpretation of Messiah's death with Irenaeus relay of the Gnostic view of the passion:
"he [the Messiah] did not himself suffer death, but Simon, a certain man of Cyrene, being compelled, bore the cross in his stead; so that this latter being transfigured by him, that he might be thought to be Jesus, was crucified, through ignorance and error, while Jesus himself received the form of Simon, and, standing by, laughed at them. For since he was an incorporeal power, and the Nous (mind) of the unborn father, he transfigured himself as he pleased, and thus ascended to him who had sent him, deriding them, inasmuch as he could not be laid hold of, and was invisible to all."
CHURCH FATHERS: Against Heresies, I.24 (St. Irenaeus)