this is so that the disbelievers among people given the book may know that they do not have any control over allahs munificence and that the munificence is in allahs hand – he bestows to whomever he wills and allah is extremely munificent.
لئلا يعلم أهل الكتاب ألا يقدرون على شيء من فضل الله وأن الفضل بيد الله يؤتيه من يشاء والله ذو الفضل العظيم