Original sentence: Arab sources generally tend to concentrate their attention in the superficial similarities (such as morphology, syntax, phonotactics, lexicon, word-formation) and to ignore the differences, and so show a culturally-biased tendency to regard MSA and Classical Arabic as different registers of one and the same language
Edited sentence: Arab sources generally tend to regard MSA and Classical Arabic as different registers of one and the same language because of the overwhelming similarities in such areas as morphology, syntax, phonotactics, lexicon, and word-formation and because the differences are much fewer than the differences extant in Modern English from the 15th century to the present