Arabic has changed far more in the 1400 yrs since the Koran tried to stablilize it, than Hebrew has in the 3453 years since the Torah was given...it is also such a LIMITED language, any attempt to teach a modern science or medical class in Arabic would just have to create a new language virtually, while it CAN be done in Hebrew, as in English.
As to whether the West-semitic language depicted on the Tablets of Ebla in N Syria (from the time of Abraham) may have reasonably represented an original Language of Abraham from which both Hebrew and Arabic sprung...well, to a degree I guess, but despite Ishmael's mother being Egyptian, there is more Egyptian loan words by far in Hebrew than in Arabic...