How can we reconcile the prophets' immunity to flaws with Pharaoh's statement about Moses, "This one who is insignificant and can hardly express himself" (which may indicate a speech impediment), and Job's illness, from which it is said people recoiled?

The prophets are the best and most honorable of people. Allah has distinguished them with virtues and protected them from major sins. They are human beings who experience hunger and ordinary, non-repulsive illnesses. Pharaoh's statement about Moses, "مهين" (insignificant), meant that he had no kingdom, and "لا يكاد يبين" (he can hardly express himself) referred to a lisp in his tongue which was removed by his supplication and Allah's response to him. As for the affliction that befell Job, it was not repulsive. The stories and Israeiliyat (Jewish traditions) that describe the prophets' illnesses in a repulsive manner are not based on legal evidence, because the purpose of their being afflicted with illnesses is to console their followers.